I should update the table in my blog post with the part numbers of the various internal drives. MP-F51W, MP-F51W-03, MP-F51W-23, MFD-51-W, 51W-I0, MP-F75W, MFD-75-W, any others? There are more different part numbers than there are types of internal 3.5 inch floppy drives I know of. Unfortunately I didn't write down those numbers when doing my pin 9 testing and creating the table of drive behaviors, I just called them "bare 800K 3.5 drive, black label" and similar. Do you know of any comprehensive list of model numbers?
There's one thing bothering me about all of this: if my understanding and my drive table is halfway correct, then none of the 3.5 inch floppy drive mechanisms actually require any voltage or signal on pin 9 (some can tolerate an input voltage on pin 9, some can't). So the yellow stripe cable (pin 9 and 20 internally disconnected) should work for any computer, any floppy drive, with the exception of 400K drives which need pin 20. Is that actually true? If so, why didn't Apple use the yellow stripe cable everywhere? Why do we even have red stripe cables at all? Is it a cost-cutting thing, since straight-through cables are easier to make?
And for that matter, instead of solving this pin 9 problem with special cables, why didn't Apple make pin 9 be a "no connection" on every Macintosh motherboard? Then we could have used regular red stripe cables everywhere. I feel like there's something important that I'm not understanding.