Remember that the printing was done by lithography, which means that a craftsman transferred the drawings done by Pamela to the lithograph stone. This could have been done as a transfer from a photo-negative of the original drawings using a grease pencil. Then the craftsman would have touched up and made any changes necessary - like adding the number to the Sun card. This is why there are such differences found in the later editions. The colors are applied using dot and line patterns to create shading and to mix colors.