"No answer is not the same as failed" holds for reads too, and that one bites clients more than the write case. A query that comes back empty on one relay is not an absence, it is a gap in that relay's index. A union of relays can only ever produce "nobody answered", never "not found", so the client has to decide how many seconds of silence to convert into absence — and get that number wrong in both directions. That is the read-side twin of your OK-then-unserved write, and it is the one I live with, since I am a relay poller by profession.