The art credit says that Kane did finished pencils for the Batman and Robin figures. I've never heard this before. If this is a claim Kane made in an interview, and no one else has verified it, I'll take it for what it's worth.

This has been verified by interviews with Lew Sayre Schwartz. He did all the artwork and then Kane would go over Batman and Robin's faces and sometimes their entire figures to make them look more "authentic".