I do not own a copy of this building, but I have a few suggestions.
Given it's a short wire, the plug can't be that far away. Look around with the mirror again. It has to be there. Your 2nd photo shows a series of plugs look at it again and make sure you haven't overlooked that empty slot.
I know it is frustrating but what other real choice do you have but to try and find it?
Wishing you success.