There may be several other varities out there as there were several re-orders over the years for both the Horseshoe as well as Joe Brown's Horseshoe. The exisitng dates of the coin inserts by casino are as follows:

Joe Brown's Horseshoe Club:
1945D, 1955D, 1956D, 1957D, 1958D

Horseshoe Hotel & Casino:
1961D, 1963D, 1964D, 1967, 1968D, 1969D, 1970D

Binion's Horseshoe:
2001D

Other dates may exist

John K. Kallman
LM112-112