New
#360
Superfly gave a list of acceptable windows 7/8/8.1 keys acceptable for 10565 direct activation a few weeks ago:
Next big Windows 10 release will ease activation hassles - Page 3 - Windows 10 Forums
I installed 10565 using the MCE key when asked for a key the first time during setup - accepted after a pause, while I guess it was checked, then the install was activated "with digital entitlement" when it completed.
The MCE had previously been used for Windows 8, then retired when I upgraded to 8.1. I have another MCE key which was never used during the period it was supposed to be eligible for upgrading 8Pro to 8MCE. I wonder if that would still be valid?
I'd also used a key from a Windows 7 Starter COA on the back of a dead netbook on a totally different desktop - which was accepted and activated on a machine which has never seen windows 7 or 8 Home edition.
Anything non-SLP seems to be accepted as a valid key for a clean install, and SLP is acceptable for an upgrade. Since the upgrade can then be clean installed, it seems kinda pointless to exclude SLP keys at this point.