A recent Court of Appeals decision has clarified the formula that should be used in determining permanent disability awards after apportionment to a prior award. In Gallo v. Dykes, the Court has determined that the famed "formula C" in the Fuentes case should be applied. In that formula, the dollar amount of the total permanent partial disability is determined and then the prior dollar amount of the award is subtracted. This decision overturns the Nabors decision by the WCAB which applied Fuentes "formula A" which subtracts the percentage of the prior award and then determines the dollar amount of the remaining percentage. In the Gallo case the difference in final PD was around $50,000.
Workcompcentral.com (archived) has an excellent article on the subject.