Yeah I saw, but I wouldn’t call them broken to begin with 
The more I think about this the more I feel it would be better to split the unit numbers per level with tags like
addr:flats:level:8=801-803;805-809
addr:flats:level:9=901-903;905-909
and/or
addr:flats:level:ref:G=1-3;5-9
Per the existing tags level=* and level:ref=*.
This will keep the tag values shorter and make it easier for us mappers too, while also adding extra data about the level each unit number is found on.
The only limitation is sometimes it would be obvious from the numbering scheme or the letter boxes alone.
The downside is this requires one to enter the building to map, which in many instances you wouldn’t be able to access. Quite different to just surveying the letterboxes from outside.
EDIT: proposed at Talk:Key:addr:flats - OpenStreetMap Wiki*