Bryan: That's one of the things I look for in undated photos. If the car has an ACI label, but no COTS, or the early single-panel one, it's probably usable in 1974. Of course, it could have been retired between the (unknown) picture date and mid 1974, the early 2-panel COTS was in use n early 1974, and it took some time to apply them to all cars. So some of the cars in my period actually had them, and some pictures that look pre-1974 aren't, but it's a good starting point.
In the case orf your models, all I have to do is look at label, or your website. Much easier!