Hello everyone.

I've been testing the free upgrade from W7 SP1 to W10 on my VirtualBox machine mainly without any intent to upgrade my live Windows 7 anytime soon, the new system still didn't convince me that it's worthwile after the screwup that MS did with Windows 8/8.1. I'm perfectly happy with Win7 as a power user (again skipping Vista because of its bloated PR and some unhappy hands-on experience), and I like the sexy rounded looks of the old system way better than the kids-crayon and all-squared style of icons and windows of the new one.

Now for my actual question:
My idea was to test the upgrade to Windows 10 and afterward a clean install on the same machine at first in a VirtualBox test environment. So far so good, all worked fine, so I've got proof that if I would decide to upgrade my live system, I wouldn't hit any walls in the process. What I want to achieve with all this is making sure I'll be able to activate a legit upgraded Win10 copy after I've upgraded my hardware, e.g. changed the motherboard and CPU to get more juice out of my desktop in the future, without having to go over the whole torture of upgrading and cleanly reinstalling to get it running smoothly without well-known upgrade difficulties.
My MSDN key says Retail channel, not OEM, and the keyfinder tool from majorgeeks says this:

Windows 7 Ultimate Service Pack 1
Product Part No.: X15-39004
Installed from 'Full Packaged Product' media.
Product ID: -censored- match to CD Key data
CD Key: -censored-
Computer Name: DEX-PC
Registered Owner: Dex
Registered Organization:

So if Retail is correct, and from what I gathered elsewhere, retail Windows will upgrade to retail Windows, so fully transferable between machines, what am I missing with the upgrade process, licensing, etc, when a fresh install of Win10 using the media creation tool and booting up from the created iso, with the key from the upgraded W10 fails to activate on a newly created different VM? And I realize that I'm trying to play wise here too, as the MSDN edition is not a real retail version, and the licensing and legality is sketchy at best, although I can prove that I've obtained the MSDN key from my company at my own discretion and this was completely legal, and I'm just fiddling with semantics and "legal" vs "practical" here.

Windows 10 keyfinder:

Windows 10 Pro
Product Part No.: [TH]X19-9
Installed from 'Full Packaged Product' media.
Product ID: -censored match to CD Key data
CD Key: -censored-
Computer Name: W10
Registered Owner: Dex
Registered Organization:

Activation error code is: 0xC004C003

Thanks for any input