It seems to me that someone who would write “OSes” would be someone who always says “OS” rather than “operating system” when speaking. The pronunciation of the plural form of “OS” would sound like “OSes”. Thus a person who never actually says “operating systems” might tend to write the plural of “OS” the same way he/she pronounces it.
As we are talking about technical literature I use Cisco press, Microsoft Manual of Style, and Microsoft Computer Dictionary (fifth edition) to know what does OS mean.
Microsoft Dictionary says: “OS n. See operating system.” And then in Microsoft Manual of Style (version 3.0) we can read “To form the plural of an acronym, use a lowercase “s” without an apostrophe.” Example: several IFSs.
So, I’m not fully confident about OSes or OSs, but I am fully confident that OSs is acronym of operating systems, but not an open source [color=red]systems, cause open source software (not system, if you mean UNIX) is OSS but not OSs.
Cause we are talking about plural form of acronym but not about possesive case.
I didn’t understand the meaning of your “research”. Did you type in search bar “mac OS’s” and “mac OSs” and compared the results?