Question windows 10 still active after full upgrade

[nsmith0723]

So me and my buddy bought all new hardware, mobo, cpu, psu, and hard drives/ssd. same cpus for now. In my case I went from Intel to and. he went fx to ryzen. Long story short we left the old hdd in to migrate data. So how in the world did both systems boot. All the data I've seen up to this point would say it should not. Legal copies btw. We got the free upgrades. Im guessing we both didnt luck out. Gotta be the hard drives?

 

[Dark Lord of Tech]

It happens quite a bit , not rare for the new setups to boot on an old HDD.