In a Windows 10 S \$Windows.~BT\Sources\Product.ini you can find all the generic Keys for the current available editions to date I guess. The S edition uses the "Cloud" Key:

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[cmi]...

Going back to the early days of Windows 8 RTM, October/November 2012, you could upgrade trial Enterprise Windows 8 versions with genuine retail ESD Windows 8 Pro upgrade downloads (I had a £14.99...