I don't feel that I'm missing anything.
You have been told the copy of Windows 7 you had is not genuine. I don't think anybody was necessarily suggesting a course of action, but rather it was meant to inform. You can continue to believe whatever you prefer. Just remember that since we know it is a pirated install, technically it violates forum rules to provide any assistance at all.
Some interesting information about the pirated Windows 7 "Extreme Edition"; it was created around ~2009, and the site can be found with a google search. The fellow selling it uses a yahoo E-mail and sells his pirate software as well as Volume License keys and Activation hacks from that website. Some portions of the site was DMCA'd by Microsoft, meaning many of the links have to go to web.archive.org. I find it hard to even contrive a scenario where it is above-board.
Now, that said, the main concern, IMO, with that version was less it's legal status (outside of course forum liability), and rather that those sorts of pirated installations tend to leave lots of fun goodies such as Remote-Access Trojans, botnets, etc.
You've upgraded to Windows 10 now, which has a good chance of resolving some of those concerns with regards to malware. It is impossible to be certain, though, which is itself a concern. Most software can "survive" an upgrade- the entire upgrade process tries to preserve it, after all.
It appears that you are taking the approach of "If it let's me do it, it is totally legal". The Windows 10 Upgrade requires a legitimate copy of Windows 7, 8, or 8.1. You did not start with a legitimate copy of Windows 7. The Windows 10 upgrade was tricked by the pirated install in the same fashion as the online tool that you posted as 'evidence' that it was genuine.
You spoke to a MS representative of some description. Explained it, and they basically said it was fine. I get the feeling that when it inevitably is not fine they won't be around to clean up the mess, and the story with any representative will suddenly be different, and they will not believe you when you say "The last person I spoke to said it was fine".
Now whether you want to be concerned about the legal status is up to you. Whether you want to care that your system is probably harbouring any number of low-level remote access trojans that Windows has been modified to never reveal to software such as MBAM is your prerogative as well. If you want to continue to use a copy of Windows 10 upgraded illegitimately through the upgrade process by upgrading a demonstrably illegitimate copy of Windows 7 which may be harbouring innumerable pieces of malware, and for which the illegitimate volume license key used for the pirated Windows 7 installation may be discovered and blacklisted by Microsoft, causing your Windows 10 copy to realize it is illegitimate is, also, up to you.
If in the future you need to create a thread titled "Windows 10 claims it is non-genuine" or something similar, just remember that "I told you so" is not against forum rules.
