Small rivet and slots, so you have the rare transition sheath.

It's possible that the guy who did the stamping just picked up the wrong stamp maybe thinking it was a 5 1/2" blade. However, if it was stamped in 1945, it's a '45 blade and not a '45 knife as the lower quillion is the normal length. Most of those very early 3's had an abbreviated lower quillion like Joe's (Just another "tell").