Thanks @alien63 for the first fact, @HashtagPon3 for the second, @Kittyhawkmc for the third, and @SnowBell555 for the last one!

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-In Fire and Ice, on page 281, Sandstorm is called Sandpaw even though she was just made a warrior.

-In Enter the Clans, when Brightheart was still named Lostface she says that "as long as I have Cloudtail, I will always be Brightheart." even though she wasn't named Brightheart at that time. 

-In A Forest Divided, the marsh is constantly referred to as the pine forest.

-Lionblaze and Cinderheart's kits are named Hollytuft, Fernsong, and Sorrelstripe.

-Brightheart doesn't go down to the lake because she doesn't want to see her face.