I don't think just 1 year passed. Between seasons it was Winter at least twice, and they never specifically said that this was the first Summer Sun Celebration since the one at the beginning of the series. I bet maybe two or three years have passed before we got to this point. Nice review tough.
Yes, but in the episode they specifically said the Summer Sun Festival where Nightmare Moon returned (and purified) was exactly one year ago. I agree as well, chronologically it doesn't make sense. They had Winter Wrap Up AND Hearthswarming Day in different episodes with Nightmare Night in between.
I don't recall, I'd have to go watch it again, which I will eventually but I'm pretty sure it was in the beginning before Celestia and Luna got taken. It may only have been a flippant comment, but I'm certain it was there