This is more a Silver Age variant question/comment but I figure it'd get more traffic and interest here. I have a Mickey Mouse 84 from 1962 in this ebay auction and I have gotten the similar question about the interior ads from three different folks.
Here it is copied.
"Q: Please inform me if on inside front cover there is a gag page of "Mickey Mouse (Pluto fans Mickey) or there is all advertisement of "Walt Disney characters by Mother Hubbard dept.N.Y. Grazie Giuseppe"
Ebay link
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=400143796493
So clearly there are two versions and I wondered if anyone was aware of this, had any info, or collected these variants. The version I have appears to be the common version.
It's also possible one version is Canadian, which would be an interesting possibility if there was a 12/15 cent Dell that also have different interiors for each pricing. And it could be shown somehow that all versions with different interiors were Canadian. Just speculating as a way to play detective.