We used DL99 all the time at LCY. Usually because Codeco wouldn't accept more than 2 delay codes so we would enter say 93 and 99 and then split 99 in the SI field.
thats because you should not have more than 2 delays. I hate it when you have late cleaning AND late catering. they may have both been late but only one caused the delay the other managed to get off the aircraft before they caused the delay. and before some one else says it the last supplier off the aircraft is not always the one that caused the delay