See fiatjaf and will’s evaluation of outbox implementations to date

nostr:note1cgmcrmeeeum78xavgpmtq69vlcfyres83q8lws6rrc6h8lr7shfsqxhah4

nostr:note1g4sm49t359s33qtfmh3l2rqxcnxxzh0pcen8flzaxcj3exydvj4q0t7y4c

It seems:

-there are various implementations, which don’t fulfill fiatjaf’s criteria of finding the notes on the smaller relay

-there is lack of clarity surrounding the “correct” approach to implementation (if such a thing exists)

-there is some tradeoff between performance, data query volume, and finding notes/events

So it could be that the full solution is somewhere, and there is no or difficult to find documentation, or there is a partial solution with unanswered questions such as the above.