Earlier quoted context omitted.
And yet these are still (apparently) implemented as search queries instead of direct database queries.
There may be some magic they do to better optimize within-user-searching. It's something that they could hide in implementation details so we can't be sure unless they spill the beans but it's feasible - especially with the default search parameters they're using. I'd still love something a bit more obvious and intuitive but if it's just a UX failure that makes me feel a lot better.
I would have believed this until last week when they had a little banner informing me that I might not see all the PRs but that they really were there and that I could use such-and-such API to find them myself.
If the direct API existed and was working, but the web UI wasn’t seeing the PRs, then presumably it meant that the web UI was not optimizing the default trivial search query to use the direct API.