I know that, besides the other plants in question ABC used, they also had their own pressing plant, True Sound Mfg. Corp. in Hauppauge, NY. You might want to check to see if any 'TSM' or 'TZM' or whatever etchings are inn the deadwax of those records you speak of. If that's on such pressings with the serrated edge, there's your answer. If not . . .