Hypothetical question re Win 10 home-Pro upgrade.

I've asked this on various Windows forums & received conflicting replies; some say it'll works while other say it won't, posting here to get a genuinely honest answer.
Long story so bear with me.
I previously has a Vista premium/pro laptop which was retired & I bought a Win 7, this came with the Win 8 upgrade offer which I chose to receive on CD which came with a Windows 8 pro key. Before I could install win 8 on win 7 laptop, it failed so I received a refund but was left with the upgrade & key doing nothing. I installed Win 8 over Vista & eventually I also upgraded Win 10 after several months of Windows 8/8.1 working fine.
Now I have a Win 10 home laptop as old one died, my question is can I use the win 8 pro key to upgrade win 10 home to pro or was it absorbed into Windows 10 upgrade on the old Windows Vista-Windows 8 laptop.
I just want to make sure before I throw the CD & key away that it cannot be used again to install Win 8 or upgrade Windows.
TIA,

First question - (and probably the only one that really matters) - did the various OS versions come pre-installed on on a system, (supplied by the manufacturer)?

If this is the case then the OS is tied to the original hardware and "dies" with that system, it may be upgraded but not transferred to another system.

If the OS you have is a Retail OS then this can be transferred as many times as you wish, as long it is only in use on one machine at any time.

Yes the Vista was pre-installed & had the key on the bottom of the laptop, when I upgraded I then entered the key which came with Win 8.

Doctor9fan said:

Yes the Vista was pre-installed & had the key on the bottom of the laptop, when I upgraded I then entered the key which came with Win 8.

What you can do is download a program made by one of our members here. Run this program on the computer in question and it will report to you the Key # and if it is a OEM key or a Retail Key. If its reported as Retail then you can use it to upgrade to Windows 10, same version Home for home ..Pro for Pro
https://www.tenforums.com/software-ap...7-showkey.html

I no longer have the original Vista/Win 8/8.1-10 laptop as MB failed, I know the current laptop has OEM version of Win 10 home.

AnEdge said:

Just enter the key and see if it takes. Make sure its not activated on the other machine. You should find the upgrade to pro on the lower portion of the System page. If it doesn't take it will say its not a valid key, and if it does work, celebrate!!

Will try that later, haven't so far as I didn't wish to mess up the original OEM key but if it just rejects the key if it isn't valid then it's worth a shot.