Quoted from blownfuse:Guess the change of the name wasn't added then. Interesting, the Carnival may have indeed been made that way and was a sample game that showed up at the fair (I assume the fair was at or after '50). They might have changed the name to Mardi Gras because the name Carnival was used by Bally in '48, Mardi Gras production started in '48 too.
Steve
To add to the mystery, the original backglass artwork for Bally's 1948 Carnival was called "Mardi Gras":