It has long been recognized that an employee's ability to participate in vocational retraining is a significant factor that must be considered in assessing the worker's permanent disability. (LeBoeuf v. WCAB (1983) 48 CCC 587, 597.) An employee's inability to compete in the open labor market could support an award of permanent total disability. Even though vocational rehabilitation was repealed and replaced with the supplemental job displacement benefit, an employee still can rebut a scheduled rating by establishing that he or she was not amenable to rehabilitation. (Ogilvie v. WCAB (2011) 76 CCC 624.) That's commonly done with evidence from vocational experts.
When defendants seek to apportion an applicant's permanent disability, most often they look to apply Labor Code § 4663, which directs that apportionment be based on causation. LC 4663 requires a physician to consider factors both before and subsequent to the industrial injury, and the courts have not limited what can be apportioned under § 4663. They have allowed defendants to apportion to asymptomatic previous conditions, risk factors and even genetic factors. The only limitation has been that to apportion under § 4663, the physician's opinion about apportionment must be substantial evidence.
Labor Code § 4664 is the other statute that addresses apportionment in the California workers' compensation system, and it allows apportionment to a previous award of permanent disability benefits. LC 4664(b) states, "If the applicant has received a prior award of permanent disability, it shall be conclusively presumed that the prior permanent disability exists at the time of any subsequent industrial injury." If § 4664 applies, the percentage of permanent disability found under the previous award will be subtracted from the current overall percentage of disability.