I just wanted to report back on this. After further consideration I am considering moving to Kevin's method. His method has one big advantage - it does not matter if a project starts with a room being called one thing and changes to the room being called another thing. Consider this not to uncommon scenario.
The bedrooms on the plan are named bedroom 1, bedroom 2 and bedroom 3. Using my method the labels will be prefixed with BED2A, BED2B etc. Now the job progresses and the Client is calling those rooms by the names of the children who will be living in them, "Joe's Room", "Brian's Room" etc. With Kevin's method you can easily update the room names to reflect what they are being called, and everyone is on the same page. With my method if you change the room name for reports, now the labels don't match the new room names. So the report might say "Joe's Room" but the room ID says "BED2A". Make sense?
So I am changing my method to Kevin's. In actuality, I was using his method from the beginning and was just testing you Graham, seeing if you would point out the the limitation of my method. Fail :p

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