Board Thread:General Discussion/@comment-4928331-20130206013126/@comment-4928331-20130208234537

It's not completely random. Whenever Batman, Superman, Martian Manhunter, Miss Martian, Nightwing, Zatanna, Beast Boy, Impulse, G. Gordon Godfrey, and Cheshire appear, their creators are automatically credited.

In the case of Martian Manhunter, it doesn't have to be him. It can be a shape-shifted Miss Martian (DEPTHS, CORNERED).

In the case of Nightwing, he doesn't even have to be on-screen (RUNAWAYS).

As for the others, there is a strong bias for crediting Jack Kirby characters and Perez/Wolfman characters whenever they appear,