Thanks dave61965 for linking the pics of the other lock. Note the frizzen spring is different. The cock spur is a little different at the top where it curls forward. The tail of the two locks are slightly different in shape and the curve in the engraved border line.
The mark on the inside of the lock has an awfully rough edge. There are pits on the metal surface around the lock that may contribute to the rough edge some, but it clearly isn't a stamp mark. These are normally investment wax cast parts that faithfully copy the original item that the mold was made from. That means the original pattern that was used to make the mold would have looked much like what we see. I've seen little bumps on wax parts similar to this when the wax cooled too quickly and/or trapped some air against the surface of the mold.
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If Eric's lock has a similar mark, then it will be good to know that Gostomski used a mark and what it is.