Here's a mystery that perhaps some fellow animation buff out there can help me solve. It involves the 1949 Tex Avery cartoon, The House of Tomorrow. The film is narrated by Frank Graham — all but for one short gag for which the narrator momentarily turns into Don Messick. Then, when they get to the next bit, he's back to being Graham again. If one studies the music and art style, one concludes that the Messick-narrated segment was done later — probably years later. There's an abrupt jump in the music, suggesting that the bit was inserted after the cartoon was completely scored. (Also, Messick and Daws Butler both always agreed that Don got his first cartoon job, which was with Tex, after Daws was already working for the director. House of Tomorrow was made some time before Daws's first work in the field. Graham died in 1950.)
Anyway, the inescapable deduction here is that the cartoon was completely filmed and perhaps even released…and then, years later, someone — probably not even Tex; probably Hanna and Barbera — went in and replaced one joke with a different one. This may have been done for a re-release. And the inescapable questions are, assuming all this is true, what was replaced and when and by whom?