I've seen a few of these around, where they've tried to include too much information behind the housenumber tag. These should be tagged eg. as follows addr:housenumber=7 + addr:unit=L and then there should be added individual entrances for each flat. The flat address should be added to these entrances behind addr:door tag. These flat details are now been listed in the housenumber tag where they don't belong. To do this properly an onsite survey should be performed to locate the entrances.
