The boot drive seems to always be seen as "C:" as near as I can tell. So when booting from USB, with a different drive internal, the USB drive becomes "C:".

But I'm no expert on MS-anything.

Linux and Mac have no problems with exact cloning of system images/drives. Fuss with those seems to be only a Microsoft obsession.

Many people I know just boot Linux from a USB stick periodically, and from there do a very simple bit-copy of their MS-Win drive to a backup device. Eg. "cat /dev/sda > /dev/sdb".

Then, should the carefully curated main MS-Win drive ever fail, a replacement of equal or greater size is acquired, and the bit copy is then done in reverse to regain an exact setup to before.