Well, the point is, it depends on how the people/community in your country define "Cosplay". I understand Cosplay in US covers as much as Costuming do BUT
in Singapore, "Cosplay" seems to entirely "restricted" to replicating Character from Anime/Manga/Games/JRock/JPop (and other Asian-Based Media
) unless its a BIG
Title like Warcraft or Star Wars or Harry Potter. So when someone start doing "That Student who is seen behind Sakura in Episode 11
" aka Generic Character, the "newbies" will start frowning upon it.
Anyhow to me, cosplaying from a Concept Art is good and should be encourage as you are trying to replicate something and am sure is putting in efforts in making it as close to the original as possible or turning your brain inside out trying to use your own creative juice to make the costume more interesting especially in the case when you can't see the remaining part of the costume (like the back or below the waist or even color
), instead of simply putting a Generic Costume together from whatever you got in your wardrobe.
So if you want to do it, then go ahead. I am a Fan of Concept Art or Illustration Costumes/Armor and had done it apart from planning to do more from LOTR/The Silmarillion, SW, HP etc etc. And like the rest said, do explain to others about the particular character and game you are cosplaying to let them have a better understanding.