Q: important Q (can't seem to find the answer anywhere; lots of disagreement): what are sharps and flats called collectively? "accidentals?"
A: that indeed is what they are called, when they are not in a key signature. so when you have to put them next to the notes as they occur, those are called 'accidentals'. Almost as if you....... 'accidentally' want a note that's not in the key signature, even though you surely did it on purpose. When it's in the key signature, set up at the beginning of the song, i don't think they are called accidentals. they are just called sharps and flats. With key signatures, sometimes i personally refer to adding or subtracting sharps or flats as 'degrees' to a key signature (in order of the circle of fifths), but that is probably not a widely accepted term for that, especially because it collides with other musical uses of the word degree