there is plenty of occasions where more than two delay codes can and should be used.
The full delay should be shown in the departure signal. So what happens if a plane is late off stand for example 30 mins.
Late Inbound 15 mins
Tech 20 mins
Passenger Convenience 5 mins
some airlines demand a full breakdown of all resons for the delay.
Occasionally 99 used while we await a report for the reason for the delay. New mvt message then gets sent with correct delay code.
99 code is very rarely used as any delay should be covered by all other delay codes.
in regards to the dly 31 comment, surely that is poor timekeeping skills if it's due to chatting on the flight deck? If they knew you that well surely they would agree to an on-time departure?
I agree that even the best of us struggle to get some a/c out within the turnaround time for one reason or other and no-one is indeed perfect.