I have seen that some fights are marked as "3 Rnd + OT (5-5-5-5)". Does someone know what does it mean? It occurs only in some fights of the "The Ultimate Fighter" show e.g. in Andrew Sanchez fight in 2016. Standard notation "3 Rnd (5-5-5)" and "5 Rnd (5-5-5-5-5)" is pretty clear but here is an additional five in brackets and phrase "+ OT".
The most probable option is that OT stands for "overtime". Overtime means that if fight ends with draw, there will be fourth round. That's why there is additional five in brackets meaning time of last "overtime" round. This is a guess coming from wrestling. Term OT exists there and means exactly that.