Sadly the game does not really tell you anything about how you get the bosses, you actually have to go to external sites to find this out. Not something i believe every average player does.

Heck the tip i got when i checked other sites before the event launched was "when you cannot finish them with weak attacks anymore, share them so others can get the bonuses too, don't be greedy." This did not really help me at all -_-

That said, my concern with DMM messing up was more about some bosses having so incredibly irregular health. Even after their announced fix, i still saw bosses with lower health than some of their lower level counterparts.