Don,
When Main Street first reopened I got their Charter Member card (No Name #1a). Since then I've been walking through the casino cleaning up the discarded and forgotten cards. I do this regularly for all the casinos downtown and on my weekends I help out the strip and off strip casinos. All this time going through the Cal and Fremont, I've never found a unnamed card by itself, only at Main Street. Same thing applies to the purple temp card, only at Main Street. This is the only evidence I can give that the no name cards are Main Street.
Although I did find a NY NY crammed into the tracker at MGM yesterday. I'm calling it a new version of MGM (with Statue of Liberty).
Tom