Oooerr.
You get strange ones where there is something like 'Somewhere Place', a row of houses that sit on an existing road with the other houses continuing normally either side of it.
Main road number 2, 4, 6 , 8 <Something Place>, 10, 12, 14 etc.
When you look back you find there was a building there that occupied the same space as the 'Place' houses but accessed from a different direction, hence why there wasn't a missing number from the Main Road sequence.
In the same way they might put a block of flats where there was previously a single house and that might become 'Grove house, 105 High street' and each flat just numbered accordingly. An address then being Flat 4, Grove House, 105 High Street' or Flat 4, 105 High Street' etc.
I wonder what the limits on adding a letter suffix when a house is turned into sub dwellings, Like what was '23 The Road' now 21a and 21b The Road? I mean, anyone ever seen it go past b?
Cheers, T i m