Posted By:
Tim Newcombbut they may be hard to find after all this time.
Very short answer to your inquiry:
Many backs can only be found with M101-5 or M101-4 but not both. Several, especially the more common ones, can be found with both, including Famous/Barr, Globe, Gimbel's, Weil Baking, etc.
Sporting News backs seem to appear only with M101-4 numbers. Someone, I think maybe Lew Lipset, claimed they had M101-5 numbers with those backs, but we're still waiting for definitive proof of it.
Tim