I used my Windows 7 Pro key when doing a fresh install of Windows 10 Pro, and it worked.
The thing is, for whatever reason, I couldn't get my system to boot off my Windows 10 Pro disc, so I resorted to a bootable USB (which I created via the Windows 10 media creation tool, which I found by googling). The thing is, I've never installed an OS off a USB drive before, let alone one I created myself using provided tools. Thus, I'm paranoid that the whole install is compromised (not because I don't trust Microsoft's tool, but because I'm worried that I overlooked something when creating the bootable USB drive, and accidentally used a tampered with file).
I honestly don't know if I'm being too paranoid or not, but is there any way to verify my install as being 100% Microsoft legitimate? (I already checked the validation status in Settings, and also did the slmgr /xpr command in Command Prompt, both of which yielded results indicating it's legitimate. But still, are there other ways?)
(To be clear: my fear is that I created the bootable USB with a fake Microsoft exe without noticing, even though I'm pretty sure I downloaded the tool directly off the Microsoft website).
To be perfectly honest, I'm tempted to redo the install using the disc.