"CAIST A VT" stands for Century Arms International, St. Albans, Vermont. They were the original importer of the gun into the USA. Their new name is Century International Arms (CIA).

M-23 GER 765 PARA = (CAI) Model 23, Manufactured in/Imported from Germany, 7.65mm Parabellum in caliber.

NSA (57) -- I have no idea what that means.