Dates
IIRC,
the markings under the (cupped) butt plate indicate the maker (letters) and production date of the STOCK, not necessarily when the rifle was assembled into a firearm. The laminate stocks in particular were typically made by subcontractors, often companies that made furniture in peacetime. The numerals indicate the date thusly:
# of day of week 1-7/# of week 1-52/ 2 digits for year, in that order.
The OP appears to have reversed the order of the info, but I “think” it means 1st day of 13th week of 1944, so late March/early April 44....?
I don’t recall the maker codes, more info could be found by searching around this forum/referring to the books