Missing Credits 13

I was looking at the credits art in the Cave Story base folder, and I noticed that all the art files are numbered, however there is no number 13; it goes from 12 to 14.
Was this a mistake or is there a missing piece of credits art?

 

The number 13 was skipped because that number is often times considered an unlucky number. A lot of cultures view that number this way, including the Japanese.