You evidently do not have HOME switches or you would have the offset to go back to.
If there is any feature on your part that you can locate, or indicate in, you can pick it up then enter those coordinates into the DRO's. A drilled hole or something. Maybe a corner that was machined during the "good" paths ....... anything ?
How did you set your initial part 0,0,0 ? Just eyeball into the stock a bit ?
Russ