Ron,
I can't say where I first learned about the evolution of the 9 mm Parabellum cartridge but the first reference that falls to hand is The Luger Book by John Walter, 1986 edition, Entry A39 Ammunition Register, part ix. There it lists DWM case 480 bottle necked, 480A bottle necked, 480B straight, and 480C tapered, the last becoming the 9mm Parabellum we all know and love.
If a 9 mm Parabellum cartridge were to be fired in a chamber bored out from 7.65 mm Parabellum I would expect the fired case to have blown out to a slight shoulder like 480 or 480A. If it were fired in a chamber bored out from 7.63 Mauser I would expect the mouth to expand to an oversized diminsion and take very few resizings before cracking at the neck. This wouldn't matter too much for throw away cases, but it wouldn't contribute anything to accuracy.
You all realize of course that DWM made a few Lugers chambered in the bottle necked 9 mm cartridge. It's the one they took to England when they tried to sell it to the Brits. All you have to do is find one in an attic someplace. But don't get too excited yet, it would have been easy for the tool room to rebarrel them.
unspellable
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