During Pinkie Pie's story of how she earned her cutie mark, her cutie mark is shown on her flank when her family first enters the silo. In the next shot it is absent from her flank and a few seconds later, she earns her cutie mark.
While little Pinkie is surprising her family with the party her cutie mark can be seen on her flank before it she finally gets it at the end of the scene.
When the Cloudsdale race begins, a pink earth pony can be seen on a cloud; in "Sonic Rainboom", Rainbow says only Pegasi can walk on clouds.
The egg Spike hatches out of is purple with darker purple spots, but in "Friendship is Magic, part 1", he says his egg was purple and green. It might be because Spike was not aware of it.
Oddly, Twilight Sparkle and Pinkie Pie's respective siblings, Shining Armor and Maud Pie are nowhere to be seen in their respective flashbacks. Though it's possible that their absences are due due to the result of Twilight and Pinkie's storytelling.
Fluttershy claims that she's never been to the ground before. However, during the song "so many wonders", she correctly identifies all the animals.