Cloned working disk, now neither will boot
I have 3 Optiplex 5050s here, one I cloned the default disk to SSD, both of which boot fine (and are UEFI, I think). The other was fully operational, BIOS is set to legacy boot - I'd guess this implies it's an MBR setup disk? The third, I have a .tib file to restore to, but having done this, it wouldn't boot, either in UEFI or legacy mode. The data (including win 10 install) that was supposed to be written was all there though - guess it just needs to be "made bootable" somehow.
Eventually I just put all 3 disks into one machine, and booted to windows on the SSD (default Dell install), and in TI2018 cloned the working disk (1Tb Barracuda) to the one that wouldn't boot (1 Tb WD Blue). As part of this it told me the target disk would be converted to GPT to make it bootable (seemed reasonable since it wasn't). Cloning went seemingly without incident, but on returning the "working" disk to the one set to legacy boot, it won't. Doesn't see it as UEFI either. The newly cloned one behaves the same.
How can I best undo this? Or better get the .tib file image that should be bootable to be so?