Hello all.

My brother's laptop is starting to need a good in-depth (software) cleaning and we might end up re-installing Windows from scratch. Currently he's running Win8.1 but we might get him onto Win10 while we're there.
That laptop was sold with Win8 (updated to 8.1). While there is a Win8 sticker on the underside, there's no licence key on it.

I have already re-installed Win8 from scratch on that very laptop a few years back, and the activation was seamless without needing to input anything because the licence is tied to the motherboard (thanks Microsoft I guess ?).
Also, I know for a fact that Win 7 and 8 OEM keys can be used to directly activate Win10 when installed from a Windows installation media (not upgraded from Within Windows). I very recently did that on a friend's prebuilt that we upgraded, using the licence key that was on a sticker on the side of the case, and installing Win10 off a USB drive.

So I guess my question is : would this work on a laptop even if I don't have a licence key to input, like it worked when I re-installed Win8 back then ? Since the licence/activation is tied to the motherboard, would it behave like if I had input an OEM licence key ?

Or would I need to first upgrade to Win10 via the assistive tech loophole to activate Win10 on this PC before re-installing from scratch ?

Thanks for any answer. Windows' activation detailed arcanes are still a bit nebulous to me.