Hi All, I have a few old HP Z210 boxes that have Win 7 Pro sticker on the box. I installed Windows 10 (Pro) and just for the hell of it, used the Win7 key *after* I installed Win10 and did 'Change product key'... and it worked!! Is this legit?? - Did HP register all their Win7 Keys to be able to be used with Win 10? If I use these Z210 boxes at a business, is this OK? I don't think I registered these keys for the 'free upgrade' that expired a few years back... - Im sure it has been asked before but, I did look through as many previous threads as I could (even the Windows 10 megathread) but without any luck.... Thanks, Kon.