Not over till the fat lady sings ... in Texas?

[Baker, John]

        In the mid-1970s or so, there was a collection of hillbilly jokes (which I unfortunately no longer have and therefore cannot precisely date) that included this line.  The story's setup was that a group of hillbillies went to an opera.  At the intermission, one or more of the hillbillies started to leave but were stopped by another of their group, who said that "the opry ain't over till the fat lady sings."  It seems likely to me that this joke, which presumably had currency before and beyond the thin paperback collection, is the origin of the phrase.

John Baker