Truthfully I don't think it mattered because the Windows 10 upgrade thing is a bit weird, I don't think it actually gives you a new key, but rather gives you a generic key that everyone has and instead registers your "hardware", apparently it also deactivates your Windows 7/8 key at the same time though so you can no longer install that anymore anyway.
It all seems kind of a bit hocuspukeus to me, as long as there is a way to keep upgrading with only a single license I'll be happy, I'm not buying a new copy of Windows everytime I upgrade my hardware.