Steve,
I will have to disagree with you somwhat. The many variations of similar looking cards at places like Harrah's, Stations, Ameristar, etc make picking up all cards practical. I will not take the time to review in detail every card I find while in the casino. That could in itself bring unwanted attention to the harvester. I will take any card I find, unless obviously damaged, and look it over for variations when I get home. I can then compare it to other cards to see if it is a new one for me. Any I do not need can go with my traders or be discarded if necessary.
Paul