Simple faults relate only to PSEU, wherein the PSEU Light and OVHD system annunciator do not illuminate for simple faults unless a system annunciator panel is pushed for recall. In this case, a simple fault, resetting the MC system extinguishes the PSEU light.
So all cases of MC on recall relate to single fault in redundant systems except the simple fault related to PSEU.
Yes there are two types of PSEUs.