I was going to type out a long response but this is an issue to which I cannot be asked to deal with. I have shortened it thus.
Knocking through walls is an issue everywhere. This can be solved by editing the buildings as appropriate. Arguably address mapping would aid in the identification of such instances, as an address may disappear or change, thus prompting a change to the building area.
My adress interpolation is correct as of the date when the survey was taken.

My biggest issue with this however is in its undocumented nature. Perhaps you could update Exeters wiki page (https://wiki.openstreetmap.org/wiki/Exeter) to inform of, and explain this better?
I have fixed the supposed issues, thereby arguably worsening the map quality.
Bear in mind the only reason I have done this is that I cannot be bothered to argue with an illogical and unreasonable position.