Since the Landmark closed in 1990, we can assume that card is from the 80's or earlier, which still makes it an early one. According to an article in Coast-to-Coast magazine (Tom Pleau), the first LV in-machine slot card was from the Frontier (Gold Rush Club) in the 1970's. Don't know if that's definitive though. Also, Atlantic City issued the first on-line slot player tracking system in 1985, in conjunction with vendor Electronic Data Technologies, according to Harrah's materials.

Of course, there are other plastic casino cards which predate the in-machine player cards, including VIP cards, check-cashing cards, etc. These are not true slot cards (ie, inserted into a slot in the machine) but tend to be collected with slot cards by many collectors.

I wrote an article in the club magazine on slot cards, just from my experience & a little research, but there's much more to discover for the serious researcher. An untapped source so far (to my knowledge) is contacting the card manufacturers and the software network design companies that sell the networks that connect the machines. Sort of the equivalent of Paulson, Chipco, etc. Don't know if any of them would be helpful, but if so, it would be interesting info IMO.