I think the planet is spinning the wrong way.
My saying The Flintstones at the World’s Fair was canonical was a joke. As a special, it’s anything but canonical. Cartoons feel free to violate canon all the time – I’m not convinced you could say “canon” really exists, outside of short-term. (Bob Clampett’s Porky Pig sure wasn’t Chuck Jones’ Porky Pig)
“Jetsons Meet the Flintstones” is a sort of special, too. Even if canon existed, I don’t think it’d be canonical.