And presumably Hanna-Barbera Co-Owned the characters or something, so made their own (characters) for certain shows like Laff-A-Lympics and certain Yogi Bear movies...
Ahh.. upon further reading, game show producers HEATTER-QUIGLEY (Hollywood Squares, High Rollers, etc.) conceived the original idea for Wacky Racers and, I guess, owned rights to the Dastardly/Muttley characters. So new characters Mumbley and Fondu were created for Laff-A-Lympics.