Really, the hints for the bottom two were even earlier: When describing how they got their cutie marks, it’s established Pinkamena Diane ‘Pinkie’ Pie worked on a rock-farm, and that Apple Jack tried (and to some extent managed) to fit in with her higher-class Orange relatives.  
AJ wouldn’t be able to pull it off without that background (the writers might still have done it like that, but it’d then be out of character I feel), while it’d be a bigger coincidence that Pinkie and AJ were (possibly) related if Pinkie wasn’t established as being from from a farmer-family.  
A scene from MMC showing them being bad at an unfamiliar job doesn’t, I feel, do nearly as much to add foreshadowing as the cutie-mark-backstories.

Well.. Aplejack didn’t make this dress, it was one of Rarity’s and Pinkie didn’t really work at the farm, they just had a family roadtrip.

Even after restoring the Elements and their bearers, Starswirl’s unfinished spell left indelible marks on destiny.

…What?