I've just started to collect Nevada slot cards. Is there a guide to which are the more desirable to collect? How important are variations in cards from the same hotel? I live in So Lake Tahoe and have found several variatites of the Caesars card when they changed from cards with holes to ones without. My wife and I found 8 different types of obverse and reverse designs and combinations. Should we hold onto these or are they to common to deal with?