When an employee suffers from a previous permanent disability, and suffers an additional permanent disability from the new injury, can the employer reduce their liability?

3 When an employee has suffered a previous permanent disability, and is again injured and suffers an additional permanent disability from the new injury, an employer's liability can be reduced by the process of apportionment. This process allocates the total permanent disability between the permanent disability caused by the new injury and the permanent disability caused by the preexisting injury, and charges the employer only with the amount of the permanent disability allocated to the new injury. (Ashley v. Workers' Comp. Appeals Bd. (1995) 37 Cal.App.4th 320, 326-327, 43 Cal.Rptr.2d 589.)