Very interesting. I'm curious what the os2museum.com can say -- if anything -- on this. A deeply technical perspective, as in knowing the actual bit-by-bit internals, can shed much more light.

os2museum.com was just recently able to trace how one particular DOS bug (more than two BIOS harddisk drives would make earlier DOS-versions hang at boot) was handled across different companies, and how and when exactly a fix made it into actual MS-DOS.

The context there was Compaq sold some of the highest-end PC systems, they were into 386/486, servers, UNIX, SMP, rackmount, RAID, etc, "IBM wouldn't sell you this stuff". So, reading between the lines there, Compaq ran into this problem first and 'fixed-it' in a backwards compatible way.

(Compaq had a fantastic reputation which they tarred with shitty consumer PCs. HPE still sells Proliants, and I'd guess they still use 'compaq screws'.)