does this mean "it's not over till the fat lady sings" (from opera) became fused with "it's not over till it's over" (from baseball) to become the use-anytime expression we know today?
i'm still not sure when and where the expression made its debut.
incidentally, singing opera involves the stomach muscles: as the diaphragm descends the lungs fill with air. for the diaphragm to descend the stomach has to expand. just like how you breathe when you're sleeping on your back. many of the "fat ladies" aren't fat, just exercising their developed stomach muscles.
a former girlfriend (!) was informed "you'll have to lose your waist" by her singing teacher.
fortunately i myself never had one to lose.