The database is writeable now.https://docs.google.com/spreadsheets/d/1BJelaDmh0FUY5BJ-5i-2pRgu8WgA4Ihf0HRAm95LvIA/edit?usp=sharing
Darkstar coined the term "Harddisk Personalities" which I like a lot.
I've added a field "AT drive type" - the values there are much like you'd have handled disks towards the end of the ST506 and the beginning of the IDE era: If you had a BIOS with no setting to "roll your own" harddisk definition, you'd try to come as close to the physical values of the harddisk, losing as few cylinders as possible. You'd hope that the drive in question was tolerant, so that a false setting for Write Precompensation wouldn't keep the drive from working.
I'm using a list of the extended 5170 BIOS for now, and I'm making those best bets.
This can of course be easily corrected to a stricter version or totally omitted.