My understanding of the rules is that only opposite is valid. I.e. "not forbidden" is not enough, OSM requires "official approval". For example, there is an official approval to use Bing satellite images, while Street view is not allowed. When you look at the other source and do adjust osm - it's already a copy. There is a known trick used by map owners - they introduce minor fake data, and if this data appears on other map - it was copied.
The only good source for house numbers we can use (I know) are Kartaview, mapillary, and, the best, local survey.