Now to stir the pot and add a few spices:
Skenny says No.5 FE serial number production occurred 2/44 and 3/44.
FE 70 built and marked 2/44
FE 298 built 2/44
FE 964 built 3/44
XXXXXXXXXXXXXXXX FE721 built and marked 1/44 XXXXXXXXXXXX
This is why I laugh at the characters who says their gun serial number was 1st day production, 1st week, 1st month etc. All serial numbers mean is that they are a way of finding problems and getting paid.
Oh! yes, and if you want to really loose sleep--the FE run had three different types of nomenclature/serial number location markings.