I wonder if one drive was configured UEFI and the other not? I don't think a mix will play nicely at all.
With Win10 there's no such thing as a legal copy on an isolated hard drive - it's the "signature" of the hardware in a system that now decides whether it can run the OS.
MS doesn't object to replacing a hard drive -I've replaced several drives that had been upgraded from Win7 to Win10 with new drives (SSDs) and installed Win10 on them without a drama - they authenticate automatically due to "digital entitlement", i.e. MS recognises the laptop has already had Win10 installed and is entitled to run it.
Gouli, I have Linux dual booted on several laptops that also have Win10. The end ain't so nigh.