In Flesher v. Workers' Comp. Appeals Bd. (1979) 23 Cal.3d 322, the Supreme Court was required to interpret the five-year limitation in the 1973 amendment. In that case the worker had been disabled by cumulative injuries sustained in employment by several employers between 1934 and 1973. The board interpreted the 1973 amendment as meaning that compensation for the cumulative injury was limited to the portion sustained during the five years immediately preceding the time he became disabled. The Supreme Court reversed, pointing out that the 1973 amendment did not limit the time period for which the worker might recover, but limited only the employers and insurance carriers who could be held liable. It does not appear that the constitutionality of the 1973 statutory shift of liability was raised in that case. The Supreme Court outlined the earlier history of section 5500.5: "Labor Code Section 5500.5 was enacted in 1951 to codify the rule announced in Colonial Ins. Co. v. Industrial Acc. Com. (1946) 29 Cal.2d 79, 82, that an employee disabled by a progressive occupational disease may obtain an award for his entire disability against any one or more of his successive employers or insurance carriers and that those held liable have the burden of seeking apportionment. Originally, section 5500.5 was limited by its express language to occupational disease claims, but its procedures were applied by analogy to cumulative injury claims as well. In 1973, section 5500.5 was amended to expressly cover cumulative injury as well as occupational disease claims. (Stats. 1973, ch. 1024, 4, p. 2032.)"