In manufacturing a lot of a specific parts that is ongoing Quality Control (QC) will grab a certain amount parts and scrutinize several parts to prove there were no slip ups and in tolerance. If all are within tolerances QC will give the go ahead to continue production. QC will continue pull random parts to prove parts are in tolerance. If a part is found to be out of tolerance QC will be stuck examining many or all until parts in that lot until good parts are constantly within tolerance then
production will continue.
With firearms it is a serious business. God forbid someone is hurt or worse du to poor workmanship.
I personally suspect that wasn't being done constantly by the initial runs by Remington. Hence, the term 'Remlins' as in Gremlins.
Most of those odd stamp marks are for assembly. Tear apart an old S&W and they are everywhere. Also, AC is correct about quality stamps as well. I have an unmolested Marlin 375 and never looked or cared about such stamps.