Some things I noticed:
1) If you save and quit, then go back in, the villagers who were at home come out and vice versa. I got to take pictures with my favs in their cute little hats :3
2) Fireworks are apparently the same color as the hats Redd sells in your town.
3) If you talk to Isabelle enough times (it's random), she shouts "Long Live [town name] !!". Then she apologizes for shouting lol
4) I realized that the Resetti Center thing had nothing to do with New Year's. It was just a coincidence XP (still not gonna spoil)
I had to TT a bit cuz I wasn't at my town at midnight, but it didn't count cuz I saved at like 10pm Dec 31st, then came back at "11pm the same day", turnips still alive and everything.
PS: If anyone wants to catalog them, I have a few
extra hats of all four colors... and the German, Spanish, American, and European items (only one of each, though). Still need to cat Korean and Japanese items; maybe later.