Shoot the first of each film type on repeatable shots, e.g. local scenery, use a low fog developer for 20% less time than recommended on box. Even if it fogs badly if it is uniform you can print though. The effective film speed will be reduced if it has bad fog as the (ISO) film speed is density above the fog/base level. Try 1/3 of a stop more exposure, initially.
Originally Posted by mark
Note Rodinal and Microphen seem reasonable for fog level although they are quite active...