Argh I live in house that's been converted into two flats. One system calls us (to borrow your example) 29 and 29A, another calls us 29A and 29B, and assorted

Argh I live in house that's been converted into two flats. One system calls us (to borrow your example) 29 and 29A, another calls us 29A and 29B, and assorted outliers call mine Downstairs, Ground Floor, Grannyflat .. It must be worse for upstairs, who are simulataneously 29A and 29B. I'm only sometimes 29A but never 29B. We also have three postcodes, but we're not sure which belongs to who. Luckily the two flats / six addresses all share the same letterbox.