Great topic. it really helps new fans to adapt with nicknames, songs, programs, ...
A help to know how to identify each of them is to go on youtube and search fancams specific, such as: "Jiyoung FANCAM STEP".
There, you can see how she was in 2011, not to be confused with hair, clothing, etc..
Like, the SeungYeon was with red hair in STEP, but this year is Hara who is redheaded, so the fancams can help it much.
And of course, always research a fan site in your country or ask for help for a Kamilia, because we've all passed the stage of: "I do not recognize any of them, for me they are all the same".