This appeal involves a dispute among three insurance carriers as to which is liable on a workers’ compensation claim involving one employer, Lane Electric Cooperative, and two successive injuries. The sole issue presented by National Farmers’ on this appeal is whether claimant’s condition is the responsibility of Wausau or National Farmers’. The referee ruled that claimant’s need for medical services and other compensation after May 23, 1977, stemmed from an injury on August 27,1974, while Wausau was on the risk. Wausau then appealed to the Workers’ Compensation Board. The Board reversed the referee and held that National Farmers’ was liable, taking the view that an incident which occurred in 1977, involving claimant’s lifting of a portable yard light, rather than the 1974 incident, was the source of the compensable injury and that, therefore, National Farmers’ was the responsible carrier.
Claimant sustained a compensable low back injury working in October, 1973, when SAIF was on the risk. The claim was accepted. Claimant experienced no significant symptoms after the 1973 injury until August 27, 1974, when he again injured his low back while pulling an electric line. At that time Wausau was on the risk. Claimant testified that he filled out the employer’s standard accident form after the 1974 incident and mailed it to the employer with his time sheet. The company records do not, however, contain this form or any record of it. There is, therefore, an issue between Wausau and the claimant whether the 1974 claim is barred because of late notice. Claimant was treated for that injury by Dr. Erpelding, his family physician, and by Dr. Collis but the claim was never processed.
On May 23, 1977, claimant experienced the low back difficulty mentioned above after lifting the portable yard light. Claimant saw Dr. Collis following this incident, although the appointment had been made previously for his continuing back problem dating back to the 1974 injury. On May 24, 1977, claimant executed a claim form, reporting that he had strained his back on May 23. General Adjustment Bureau (GAB) provided claim service to *807National Farmers’. GAB denied National Farmers’ responsibility for this latest incident and for claimant’s continuing need for medical treatment on the ground that they were related to his industrial injury of August, 1974, before National Farmers’ insured the employer. Wausau in turn denied responsibility on the ground that claimant’s problems resulted from the 1977 incident rather than the August 27, 1974 incident.
Dr. Hirons examined and treated claimant from June 18 to August 1, 1977. On June 18, 1977, Dr. Hirons causally related a condition he diagnosed as "sciatica” to the August 27, 1974, industrial injury when pulling the wire. But on March 27, 1978, Dr. Hirons reported:
"In reviewing the chart of Mr. Scofield, it would be consistent to say that this man had an injury occurring in 1974 and that he has had discomfort off and on since, and that he has some aggravation of this injury leading to his visits with us starting in June 1977, and going on from there.”
On May 23, 1978, claimant was required to undergo surgery for his back condition.
Claimant requested a hearing on the denials. SAIF was joined as a necessary party to the proceedings. At the hearing Wausau raised the issue of the timeliness of claimant’s claim. The referee found that claimant sustained a compensable injury on August 27, 1974, and that his claim was not barred by reason of untimely filing and remanded the claim to Wausau. Wausau sought Board review. The Board reversed the referee’s order, upholding Wausau’s denial, and remanded the claim to National Farmers’. National Farmers’ appeals to this court.
A threshold issue is raised by Wausau, asserting that National Farmers’ appeal should not be considered because of its failure to follow Rules of Appellate Procedure 7.17(f) and 7.19 in not making assignments of error and by failing to set out verbatim the pertinent portions of the record to be reviewed.1 Because our review in workers’ *808compensation cases is de novo, assignments of error, while desirable and extremely helpful, are not required. See Patterson and Patterson, 286 Or 631, 596 P2d 554 (1979); State ex rel Juv. Dept. v. Moyer, 42 Or App 655, 601 P2d 821 (1979), rev den 288 Or 633 (1980). As already noted, the sole issue is whether claimant’s condition is the responsibility of Wausau or National Farmers’. Under these circumstances we find no violation of the cited provisions of our rules.
We now turn to the merits, and, based on our de novo review of the record, we agree with the referee that SAIF has no responsibility or obligation with respect to claimant’s claim for his disabling back condition. The claim accepted by SAIF was a non-disabling compensable injury, which required the payment of medical benefits only, and has no relevance to this case.
Next, we conclude that claimant has proven by a preponderance of the evidence that his claim for his disabling back condition which required surgery in 1978 is a compensable claim against Wausau, employer’s insurer in 1974. See Calder v. Hughes & Ladd, 23 Or App 66, 541 P2d 152 (1975). Also, claimant’s testimony, supported by the *809testimony of his son, showed the fact of the accident in 1974 and also established chronic symptoms following that accident. Claimant’s testimony, supported by the testimony of Mr. Newland, employer’s office manager, established the fact that claimant’s chronic symptoms worsened with the passage of time from August 27, 1974, to May 22,1977, the day preceding the May 23, 1977, incident. Claimant’s testimony in this regard is also medically confirmed. He was examined and treated by Dr. Collis on December 1, 1976, and made a return appointment to see Dr. Collis on May 24, 1977, without regard to the then unknown May 23, 1977, incident. Also, during late 1976 or early 1977, claimant inquired of Mr. Newland about the status of the claim which arose out of the 1974 event, because his condition was worsening and because he wanted to know who would be responsible for continued medical treatment.
Wausau places great reliance on a statement in an opinion expressed by Dr. Serbu, the neurosurgeon who performed the laminectomy in 1978. In its brief, Wausau states:
"Claimant was referred to a neurosurgeon, Dr. John Serbu, on August 17, 1977. Dr. Serbu examined and treated Claimant several times over the next two years. Initially, Claimant did not report the May, 1977 injury and Dr. Serbu was of the opinion that Claimant’s problem was related to either the 1951 laminectomy[2] or the 1974 injury. But on May 15, 1978 when Dr. Serbu was informed of the 1977 injury, he concluded, on the assumption that the incident had in fact occurred, that 'obviously one would have to relate his present symptomatology more to the 1977 injury rather than the 1974 injury.’”
Dr. Serbu first examined claimant in consultation on August 17, 1977. During 1978, he treated claimant. On March 30, 1978, Dr. Serbú reported that he felt claimant’s problem, the disabling back condition, was related to his 1974 injury, but on May 15, 1978, he related claimant’s symptomatology more to the 1977 injury than the 1974 *810injury.3 Apparently, when Dr. Serbu prepared his March 30, 1978 report he was unaware of the May 23, 1977, incident. On July 31, 1978, the doctor reported, in part:
"When I first saw this gentleman on August 17,1977 he did relate an injury in 1974, but did not indicate any injury in 1977 nor did he tell me that he saw Dr. Dennis Collis. He indicated that he was seen by Dr. Loescher of the Eugene Hospital and Clinic, Dr. Hirons, and also a psychologist.
"Thus I personally have no knowledge of an injury on May 23, 1977. I would feel once again that this is very difficult to organize chronologically and etiologically. Much of the decision would have to be made by reviewing Dr. Collis’s record to decide whether the stated injury of May 23, 1977 aggravated the condition which Dr. Collis had seen previously. If it did not then I would feel that his whole problem is related to his 1974 injury.”
*811When the above comments by Dr. Serbu are considered in the full context, we do not find the May 15, 1978, letter to be persuasive on the causal relationship involved here.
Lastly, we conclude that claimant’s claim is not barred either by his alleged failure to give timely notice under ORS 656.265(1), or because there is no legal aggravation claim. Claimant’s testimony indicates that he filled out the company’s standard industrial accident form and mailed it to the company office with his time sheet. There was some evidence that other documents pertaining to employes were also missing from, or could not be found in, the employer’s records. Under Oregon law, there is a disputable presumption that a letter duly directed and mailed was received in the regular course of mail. ORS 41.360(24). The presumption .in this case has not been overcome by other evidence contained in the record.
Furthermore, claimant is not proceeding on an aggravation claim. His claim for compensation is a claim related to chronic problems which arose out of an original claim which was never processed and of which, in our opinion, the employer had notice. The arguments advanced by the dissenting opinion overlook the fact that claimant had problems with his back and leg which bothered him continuously following his 1974 injury; that he had already made an appointment to see his doctor about his back at the time of the May 23, 1977, episode; that he went back to work the day following this incident and kept his appointment with Dr. Collis that day; and that claimant’s medical findings were not changed in any way by that incident.
From the foregoing it is manifest that this is not a case for the application of the last injurious exposure rule.
Reversed and remanded with instructions to reinstate the order of the referee.
RAP 7.17(f):
"The appellate’s brief shall open with a clear and concise statement of the case which shall set forth in the following order under separate headings:
*808««Sf! * * * *
"(f) Any other matters necessary to inform the court concerning the questions and contentions raised on the appeal, insofar as such matters are a part of the record, with reference to the portions of the record where such matters appear.
RAP 7.19:
"Each assignment of error shall be clearly and succinctly stated under a separate and appropriate heading. The assignment of error must be specific and must set out verbatim the pertinent portions of the record.
"The arrangement and wording of assignments of error, so far as applicable, together with reference to pages of the transcript or narrative statement, shall conform to the illustrations in Appendix F.
"Where several assignments of error present essentially the same legal question, they shall be combined so far as practicable.
"In the court’s discretion, alleged errors of the trial court will not be considered on appeal unless regularly assigned as error in the appellant’s or cross-appellant’s opening brief, except that the appellate court may take notice of errors of law apparent on the face of the record. Similarly, assignments of error which the court can consider only by searching the record for the proceedings complained of will not be considered and a brief not complying with the rules may be stricken.”-
According to the record, in 1951, claimant had lumbar disc surgery for low back and leg pain at the Veterans’ Administration Hospital in Portland. He had good results following this surgery and was able to return to work until his 1974 injury.
"May 15, 1978
"GAB Business Services Inc. Suite 3
2130 S.W. 5th Avenue Portland, Oregon 97201
"Re: Dale E. Scofield
File No. 49318-22419
"Gentlemen:
"Mr. Dale E. Scofield was seen in my office again this afternoon at the request of Doctor Hirons.
"Recently his claim was presumably denied. The patient claims that on 5/23/77 he did see Doctor Dennis Collis after injuring his back while unloading some material from a truck. I personally have no record of this injury, but I am certain Doctor Collis would have such a record if this is true. If that statement is true, then obviously one would have to relate his present symptomatology more to the 1977 injury rather than the 1974 injury.
"In any event, he has again developed severe left leg pain. His straight leg raising test is very abnormal, etc.
"I discussed the entire situation with Mr. Scofield and indicated that I could not say whether he would be picked up as an industrial case or not. He claims that in any event he would like to know if anything can be done to help his problem. He is thus scheduled for a myelogram on Monday, May 22, 1978.
"Any further decisions your company may make would be sincerely appreciated by our office.
"Best regards.
"Sincerely,
John Serbu, M.D.