I don't think there's anyone who doesn't know IBM finished DOS for MS and they partnered on OS/2, which means they would have agreements to share/license code/patents/methods/ect.
THOSE agreements only covered THAT technology. You really are exposing your lack of understanding on these topics, so please continue.
Somewhere I have a 180K single sided floppy.
The label says "IBM DOS V 1.0" or some such.
It is an IBM product, and they have full rights to it.