Cinderella Castle [no possessive] like other Fantasyland attractions at the time, is more based on the idea of the story, than a literal translation of the cartoon. The designs of the characters on the mosaic don't match their movie counterparts either, although the fountain and some sculpted pieces of the mice and birds do.
In the 70s, if you wanted to watch Disney movies you had to wait for a reissue or TV broadcast to do so. The closest other option would have been those storyteller records, or Big Golden Books which also sometimes took artistic license. Most people only had some memory of what the characters and scenes looked like. It wasn't important or relevant if WDW looked the same.
I blame home video and its related merchandising for setting up the expectation that Disney World would look 100% like the movies.