The example loss detection algorithm in Appendix A of RFC 9002 assumes that packets that arrives out of order are always acknowledged immediately. Because of this, it does not include max_ack_delay when the loss delay threshold is computed.

Setting the Ack-Eliciting Threshold field in the ACK_FREQUENCY frame to something else than 1 implies that some packets that arrive out of order will have delayed acknowledgments. Hence, the max_ack_delay should be added to the loss_delay variable in the algorithm above in those cases.

It would probably be valuable for implementers if this information was included in the document.

See also the quicdev Slack thread: https://quicdev.slack.com/archives/CTDAH4H71/p1725960809852329