Ronald Tyler published a catalog of Gem cobs a few years ago.  He also
sold boxes and labels for cobs, and would help identify them.  I don't
know if he is still into that or not.  He can be reached at 1076 Loraine
St., Enumclaw, WA 98022, phone 360-825-2294.

More recently, Kevin McElhone produced another cob catalog, I believe
more complete than the former.  His address is 159 Beatrice Rd.,
Northants NN16 9QR, England.

Fritz Gellerman