freebeer
There is no rule forbidding using anonymously submitted information.  See above:
comments from anonymous users which SHOULD be
Note the word is not MUST, nor MAY.  Therefore it is but a guideline.
What we  *can* act on is what you have in fact done, mapping the houses in the location.  Often that will show the marker is poorly placed, in any case I ask the contributor  to add the housenumber where correct after registering, or to open a new Note on the proper building.  (Usually with no followup).
In this case its straightforward as you drew one of only two houses visible, smack dab at the marker.
Now, how you want to go about the housenumber is your call.  If you can see it matches non-public data that cannot be directly added to OSM, that's good enough for me, as your primary source of the info was the presumed resident and it passed the not-obviously-bogus test.
(I don't think any competitor to OSM is going to put false housenumbers of new construction into their datasets and open anonymous bug-reports in the hopes of entrapment.  Not worth the bother, what do they gain?  The bad data then gets deleted.  That's normal.  No money changes hands.  Our documented trail shows the data came from an anonymous note, not from you copying a forbidden source.)
In this case, even if I couldn't verify the housenumber, it probably  is reasonable with nothing nearby to cross-reference it, so I'd go ahead and add it in this particular case.  At worst it's wrong, not bogus, and the anonymous contributor's  benefit is to have  a correct address for routing, which is obvious and commendable, unlike parks and walkways for PoGo advantage.
I write this lengthy verbal vomit as another interpretation of ``our rules'' for the community to ponder and debate.  Yes, there are lots of anonymous bug-reports like this all around.  Yes, it would be great for everyone to join OSM and add their own and nearby addresses, but not everyone can be bothered, so it's a tricky balance between expanding the community or alienating one individual, or being responsive and potentially increasing respect for OSM, but maybe encouraging people to count on submitting even more bug-reports to get things done.
Sorry for this lengthy followup.