how to spot fake parts?

i have made an interesting discovery in the attic of mystery. i have basically finished the BPT sorting, and have moved onto the vintage dark blue. will get photos tomorrow at some stage.

i wasnt going to bother looking at the dark blue at all, but curiousity got the better of me, to find many tracks stamped exactly the same as the "knock off" BPT.
my theory, since the dark blue wasnt really around for that long, the early molds werent trademarked. once they started adding the logo, they either stored or sold the original molds, and they were used to create the unbranded BPT.

i am not going to return the unbranded BPT to the attic, as i have so much and it simply isnt needed, but the unbranded dark tracks are staying.