New
#100
Whether online or manual either the Windows.old is created new when none exists or the existing one is overwritten as the existing folders are backed up over the previous. That is what prevents say 7 or 8.1 from being restored if you upgrade one 10 build to the newer. For the 7 desktop upgraded to 10 TH2 the RS1 update reported not being able to revert back to 7 once the updated build was completely on in the warning message as the manual update was first started up.
The change log only indicates the minor changes between the 14393.10 update as a general release type build and the just seen previous RS1 Insider builds including the 14393 build just seen a week or so ago for those who follow the Previews. It won't make much sense for anyone who is now either updating from the TH2 or just getting into 10 for the first time.
Did you upgrade from 8.1 Home to Pro after getting the machine? That would be the only explanation for the embedded Home key in bios problem. Otherwise it would certainly be a stranger then science fluke for 10 Pro to downgrade to Home out of nowhere during the update's upgrade.