Firstly, welcome to the confusing world of vintage Robeson pocketknife collecting.
Your knife looks great, but there is something not right about it.
The pattern number 623671 denotes a knife from Robeson's MasterCraft series and it should have a MasterCraft shield, not a PocketEze one.
First thing to do is to look at the very ends of the blades tangs to see if the bronze bearings that MasterCraft knives had. If they are not present, does the knife open and close in one fluid motion or do they catch at two or three points between fully closed and fully open?
If the blades have the bronze bearings or the blades catch, as described, then the cutler put the wrong shield on the knife, most likely.
If the bronze bearings are not present and the blades open smoothly, then the blade has been stamped with an incorrect pattern number.
Such errors occurred at probably every cutlery factory, with thousands of knives being constructed from tens-of-thousands of parts moving about in wooden trays, falling here and there and being left lying about between pattern runs.
I use to own a mint example of a 623671, but I have sold it to a fellow AAPK member and would not feel right posting its photo here. Maybe he will chime in and show you his knife.
As to the tang stamps being different on the blades, that is typical of Robeson. You will encounter very few Robeson knives with the same stamp on every blade and most of them will be premium pearl handled multiblades.
Only the master blade stamp should be used in trying to determine the age of a Robeson knife. The stamp on your knife has been dated 1916 to 1939 by Tom Kalcevic. Whether that is totally accurate is not known. It is based solely on his personal research. However, it's the best, most researched information available, so I use it.
The knife has been used and sharpened. Robeson did not make a knife with a blade bellied like that.
DE OPPRESSO LIBER
"...Men may spurn our appeals, reject our message, oppose our arguments, despise our persons ___but they are helpless against our prayers. "