Just found there was a second variation of the black Class of 55 slot card from the Morongo Casino in Cabazon, CA. There's a slight difference in the font used on the back text resulting in a very slight difference in the text spacing, etc. The easiest way to tell the difference is in the width of the web address (www.morongo.com) that is 22mm wide on one version and 23mm wide on the other. The shorter web address ends at the left of the "S" in "SPA" while the longer web address ends in the middle of the "S" in "SPA".
Here's a scan of the common front followed by scans of the different backs, the narrower web address first followed by the wider web address.