I've missed a DH on a plane I brought in myself once. Delayed by 6 hours for a "simple" TPA turn out of JFK. Got an ACARS halfway to TPA that they found another crew to fly the return leg and we would DH to stay legal. Land in TPA, crew hops in and wants to go home in a hurry since their 4 day just turned into a 3 day. Gate agent says were not listed so we call scheduling and they say they'll take care of it. Gate keeps checking while they board. Still nothing. Gate and flying CA say "oh well" and close up without us.

It only gets better. Call scheduling, tell them we missed the DH. They say we will overnight then DH on a 2pm flight home. I ask if there is an earlier flight and they say there is a 7am but its going to cancel any minute now since the pilots they reassigned to operate my original flight are no longer in TPA to work that leg. I ask if we can do it just to get home early as possible and they put me on hold because I'm legal but have to check with their manager before they can change me from DH to operating. Then manager comes on the line and thanks me profusely for agreeing to operate a flight because they hadn't thought to use us for the 7am.

Good times!