There was an early Casino Guest paper card listed in the slot guide that was also used to track casino play. An older Hotel Guest paper card was just found that is similar and also used to track casino play.

Scans of the new found paper card are on the ChipGuide now
http://themogh.org/cgupdate/cg_showpic.php?pic=../cg_pix/nv/122147.jpg&picr=../cg_pix/nv/122147a.jpg