Jake Soper makes/made (we use an archive and Jake also now designs specific shirts we are looking for) the drawings and I (Melissa O'Sullivan) design them into Illustrator pretty much as is. I do make changes as you can see below from the first panel to the second, as any editor, collaborator or production person would. I make the images usable for the silk screening process by solidifying the line work. I try to bring out the maximum potential of the images with minimal changes. Then I color them in or add a fun background or comical typography.
This is a SMALL historic sampling to give an idea where we started and how Jake and I work together - we have come a LONG WAY!