[B. Dudley]

It could be that the Serial numbers were changed.

The reason why you see odd looking things like this on Repros where the serial numbers have been altered is because the numbers are stamped pretty tight to the lug and right on the braze joint for the barrel lug. This makes getting a good weld near impossible since the brazing will contaminate the weld. So people resort to other solutions like grinding and milling off the numbers in order to re-stamp.