The last line is the most interesting, "In October 1980, Microsoft's Paul Allen contacted Seattle Computer Products and expressed interest in reselling 86-DOS. The first version of 86-DOS licensed to Microsoft was 0.3. In July 1981, just a month before IBM PC was announced, 86-DOS was sold to Microsoft and renamed to MS-DOS."

IBM reached out to Microsoft sometime in 1980 about an operating system, so SCP would've had at least 8 months to look into why Microsoft wanted their DOS before selling it entirely to them.

Did Microsoft resell 86-DOS to anybody before changing the name to MS-DOS? Did SCP make any effort find out why Microsoft wanted their DOS?

I don’t remember anyone saying or writing “eighters” and “sixers” back then.