I'm also confused on this concept, as most of the series I love are already over. I also don't think anyone at a convention is going to pull you over to yell at you for "disgracing" fans with a character they'll never see in another "new" episode again. So really, don't listen to them and do it since you want to cosplay the character and you worked hard.
-Holiday Matsuri 2016
-Joker (Alice in the Country of Hearts)
-Klaus (Story of Seasons)
-Madoka (Madoka Magica)