Vietnam era colt magaine?

I won at auction two of these magazines. they are genuine colt 20 rounders and look like the right patina of the early style. I was wondering if any one knows if they really are Vietnam era or would the later? any way of telling really?
I took one apart to get some markings. check the pics.( the first pic is like two NNs in a circle with the number 37)

The true “early style” M16 magazines were made out of steel and had a waffle-like pattern on the sides of the magazine box. The performed very badly and when the aluminum magazines became available, the military destroyed most of them with a passion, is what I have heard. At any rate, they are very rare.
I was lucky to find two of them when I was collecting U.S. Military Rifles. We converted AR15s to look as much like various “black rifles” as we could - M16, M16A1, CAR-16 (don’t recall the official name of it, but it was the predecessor to today’s M4 carbine). All semi-auto of course. I had a pretty good collection of accessories then, including Mags of different makes, of which the early ones with Armalite floor plates were may favorites.

I don’t recall my Colt magazines, of which I had 8 or 10, having that trade mark “UT” or “TU” on the back. I am not sure if the Colt floorplate really is original to that follower and magazine box or not. Will take someone with time to look it up in one of the good M16 books or expert in such matters already, which I am not, being a dozen years away from the final days of my rifle collection.