[Arran]

It's possible that the terminal box, with all of the high voltages present, may have had a cover at one time, it's also possible that the cabinet originally had a solid or a mesh back like some Radiola console models did, my Can. Westinghouse model 89 was such. It's hard to believe but even before the overly litigious and regulated society got going manufacturers of electrical products were concerned about safety, in the case of electric irons and toasters the power cords were actually a lot better then they are now.
Regards
Arran