I'm sure somebody with more expertise will come along, but I think they've shipped out ones that don't have a Colt base plate, not to mention if they are G.I. surplus it would be quite easy to have base plates swapped around. When I was in, we didn't really care what base plate was on which magazine. That' was way back in the early-mid 90's though.
Not unusual at all to have been swapped or replaced over time, they are easy to damage. They are interchangeable, I've bought hundreds of USGI surplus mags with the wrong base plates.
Screw me once, damn you, screw me twice, I'll hide your body.
I've got 2 of those ban era mags I picked up at a local surplus store (when you couldn't buy 'em). They both came with Okay baseplates. They also had the paracord/duct tape "mods".
I bought a tub of old mags recently. Several Okay mags are stamped externally 33710 and 5-91 to 10-91 but do not have the Colt or LE/GOVT/EXPORT markings. All the other Okay mags were stamped internally with 86 to 91 dates, but no external markings. Hope this helps.