I finally had a chance to check Handrich's excellent reference.
A grand total of 116 MKb42(H)s were manufactured in 1942 (apparently excluding the prototypes sent to the Infanterieschule in April) and production didn't begin until November. Troop trials did not begin until April of 1943 when the first 2000 were shipped to HGr Nord.
I would guess this entry is for a 42 dated MP40. Whoever recorded the entry simply confused the date for the manufacture code, maybe an ayf or fxo which have large dates and smaller codes.