Original cover to Modeling with Millie # 45 featuring Stan Goldberg's Millie figure.
In an email Roy Thomas explained that he never had the Kirby art, which was on an overlay. Roy also found it odd that Kirby did the correction, but as he noted, Stan didn't have many options at the time. Kirby probably happened to be in the office when Stan needed the correction, and Kirby likely knocked it out in the time it took him to light his cigar. Now, it would have been interesting if Ditko had been in the office instead...
You can read more about Millie, Stan G and Jack at my original post: