Not sure if i would call it "Grab Bag" assembly, parts were machined and put into a bin, assembler normally just reached in and took off the top.
Sometimes frames hung around for years after they were serial numbered.
Good friend of mine who used to work in Winchester's Custom Shop told me once that it was not all that unusual to have a 4 digit serial number M21 come thru the shop and this was late 70-early 80s. Keep in mind, the last M21 frames were actually manufactured in 1940, Winchester kept producing them well into the 80s.
As to the OPs original question, I've CCH a number of Winder Musket frames, as well as weld on them, machine flats on the front ring etc... no issues
V/R
Mike
