Chubb’s famous 128 Queen Victoria Street premises were indeed destroyed during an air-raid, in 1940 if memory serves me right.
I think they had two strong rooms, both of which were basic in terms of strength and security.
‘Standard quality’ and ‘Book room quality’ spring to mind, And amazingly both held up and basically saved the company by protecting all their records.
Proving the plate is one of these actual ones removed, assuming this is the story the seller is referring to, would I imagine be the tricky part, but its a nice example whatever its history and makes a change to see different from the usual brasses- a good find.