I find lots of comics on GCD where Clark Williams are listed as penciler, and or inker with a ?, as Clark Williams was a house name, used by Witmer Williams, according to WhosWho, I wonder if it was used as a true "house" name by several artists, or if it only was used as an alias by Witmer Williams?
I guess that where Clark Williams are listed as possible/probable artist, that this would mean Witmer Williams, as even if Clark Williams was used by others, he would be the artist somebody would think of when refering to Clark Williams, but are a bit curious anyway.