Cupcake - 4* Dark / Purple from Mighty Pets was released on 3rd of November last year. While you are correct in thinking they should not be available due to the 6 month rule this is BETA info on the Dark Contest of Elements event. By the time the event reaches the live game Cupcake will be beyond that 6 month window.
Peppermint was released on the 1st of December last year so unless the event is delayed in beta then it is just a little to soon to see Peppermint in this instance of the event.