I use OSM maps offline. Online OSM maps show that there are 18 zoom levels, but if I'll try to download it only offers max zoom level 16. The problem is that OSM maps display housenumbers in zoom level >16 so there are no housenumbers in level 16.
Some time ago, I was able to download maps in zoom level 17, but not aymore.
Some time ago, I was able to download maps in zoom level 17, but not aymore.