How canonical is it that the Beevers Master is the same incarnation as Delgardo?
I cannot remember where I read this. It's probably not canonical, but I don't read much non-canon DW material. It might be from the novelization of Deadly Assassin. But, I seem to recall some source indicating that the Master was burned and deformed during his alliance with the Daleks. That the Daleks turned on him. He managed to escape barely and was unable to regenerate. Of course, Delgado's last story revealed he had an arrangement with the Daleks.