Neither have I though I've always wished I could know how they did it … aside from hours and hours of looking and matching signed work to unsigned work.
We know from interviews that artists themselves were instrumental on tipping collectors off to what distinctive features can be used to differentiate their work from other in the same studio. IIRC, Marc Swayze would know his work from his colleagues from how the ears on the characters were drawn.
At Atlas, Werner Roth's work is distinctive from the shape of the characters' faces (slightly elongated).
In some Dell Westerns, how hats or horses are drawn are helpful tips in distinguishing some artists apart (or so claim some indexers on the GCD).