i never bothered to actually memorize the facts about schnorr signatures
it was registered in 1989/90 and expired in 2008
it could have been used in bitcoin but it had seen little real use in the field and there was few implementations
i just use these things... such details don't matter a lot beyond "is this correct implementation, ok good"
but schnorr would have made it possible to simplify and make bitcoin much more secure and less vulnerable to a plausible argument for changing the protocol, that point is correct