I don't know of any "standard definition" that defines the difference between a "last ditch" rifle and a late production rifle.
people can, and do call any Arisaka lacking all the initial features "last ditch", but to me "last ditch" means exactly that, the very last ones made, in desperation, substandard and dangerous to the user.
Late production rifles, without the early rifle features are not, to me, "last ditch", but lots of people call them that.
If you know a reference that states "type 99s made after XX/XX/45 are "last ditch" please share it. Otherwise, its just the opinion of the guy writing the hang tag to sell it....
I've read (somewhere,,,,
) that there was one Japanese arsenal that was still producing type38 6.5s at the end, or nearly to the end of the war....
like a lot of things, different arsenals made changes at different times, some only dropped a feature when they ran out of the needed parts.
One thing to be aware of, if you're actually shooting Arisakas, is the multi-piece wood stocks. The wood may look good, and actually be ok, but sometimes, the old glue lets go, like during recoil. I've had this happen. Not saying it will, but its something that can happen.
Elmer's carpenter's wood glue, some clamps and proper curing time returns them to shootable condition.