Do the instructors you list have physical locations that can be included? For example, the local office they all operate out of, or a home / business address each instructor works from which they are happy to have public?

I don’t think OpenStreetMap, at a base level, would accept data that is a general area of driving instructor availability, such as “Ted, Cathy and James are available within the Bridgwater area”.

Congratulation on releasing Potlatch 3 :)

Does Potlatch 3 make use of the Name Suggestion Index at all?

In your case Sophie, I would say your building wouldn’t have an addr:housenumber tag if the building itself doesn’t have a number (or a name?), and would simply be tagged as:

addr:flats 1-150 (if your block is from flat 1 to flat 150, for example) building:flats: 150 (if the block had 150 flats)

… or, if flat 13 doesn’t exist:

addr:flats 1-12;14-151 building:flats: 150

.. or, if your block only had some of the property numbers within the street…

addr:flats 130-140 building:flats: 10

I have asked Currys, and they tell me not all Currys PC World’s currently have a Carphone Warehouse in store, and that it wouldn’t necessarily be the case that every outlet ended up having one once the Carphone Warehouse branches have closed.