As Issued 1944 IBM M1 Carbine

[firstflabn]

We will never know.

Ahhh, the last ditch defense, invoked after the preferred theory falls on hard times. Even if all things are possible, it is not necessarily true that they are equally likely.

I summarized info from a WWII order that could represent thousands, or tens of thousands, maybe even hundreds of thousands - of similar modifications. However many it was that got rear sights replaced, all (or almost all) would have shown both the chisel and round punch marks like our example here.

That's the big picture. More narrowly, you might want to find CCNL-345 and -378 which detail two late, late IBMs with factory adjustables. (Hint: they don't help your case)