I'm not much help but I did buy two factory Colt mags with those baseplate markings...the metal was all more "blue" as opposed to the pictured flat look..as new mags last year.
I believe the post 94 mags will be stamped with Colt's name and mo/yr date on the side of the magazine body and the "LEO Military use" etc on the other side. Newer ones will have plastic follower instead of the metal follower like yours.