Not an unlikely scenario given it's locale, and the type and spread of damage would fit in with that theory. What we do know for sure is that it was badly damaged and yet retained. Wherever it was stored it was indoors and protected from the thick dust and grime which can accumulate on the surface. This is at the very least 117 years old. No verdigris. My guess is it was wrapped in fabric and all but forgotten in a drawer or cupboard.
I'll pop back and have a chat with the store owner, see if he can remember any detail about finding it. Right now all I know is house clearance and that the seller does perform a lot of house clearances at the request of family members of the deceased.
Meantime I still have a bit of a learning curve to repair the break. I won't be over restoring this but would like to get those two pieces reattached.
Good news so far: I went to the location, and the booth is still there. Two of them, in fact! But, it was early, and they were not yet open for business. Perhaps I need to go back, with my pickup truck and a tool box, and say "Do you want me to remove those right now, safely?" to the owner (if he is the man I have seen there before). One booth even has a cradle for a phone book, still in decent condition.
I thought that I could simply swap out the singular RJ11 wall plate for a dual jack, but it seems that the two are not connected in the back and remain separate. Is there a way for it to work without running additional wiring?