You can "kind of" determine when the 101 crankcase is manufactured by the crankcase ventilation hole. Does it have just one big hole between the cam compartment and crankcase, then it is manufactured about 1930-31.
I believe, almost certain that 1500-2000 engines in the very last batch of DGP motors got the new version of ventilation, but if they were sold as 1929 or 1930 bikes is not clear as the factory did have the device at the time "no yearly models, only constant improvement" so the manuf. year is not written in stone, but it is a hint. Anyhow the consensus today is that engines/bikes as year models 1930-31 are stamped EGP.
A batch of those late DGP engines got a nickel plated steel cover plate over the ventilation hole on the left hand crankcase, but later on the left hand crankcase are blank, undrilled.
Replacement cases for broken engines could be ordered from the factory stamped with the factory font stamp and same number that was in the registration card for the bike.
Of course with replacement cases it could sneak in mistakes in numbering or lettering by the guy/girl that did the stamping, the spare parts was taken from a pile of old stock in a later year, unclear order text had to be interpreted, and stamping was done probably not by the seasoned regular person out on the production line. Maybe that is what you have, a replacement case stamp mistake?
Unstamped cases can be found out on the market so that must have been sent to shops and dealers, probably intended to be stamped by some representative dealers with factory stamps. But as years went by, factory went bust and stuff changed hands went to be stamped in independent shops and by owners with what at hand, so some funny font stamp letters and numbers can be found. All bodged stamps does not have to be thievery or intended illegal from the beginning.
