Most of the hats, if not all of them, are taken from classic.
I made the bunny and chihuahua hat before I was hired. They were hats I made back in 2011 and submitted though a guild I was in that was owned by Trigger (who, at the time, was the graphics administrator). They were sold in 2011 for easter (bunny) and cinco de mayo (chihuahua). Granted, the hats are old and they suck because I made them around the time I was first starting out with pixel art, but they're still something of mine that was used without my permission.
and in case you want proof, I went and dug them up from the bowls of the server:
As for the rest, I've made this to simplify:
Attachment 18767
What's circled in
red are my hats.
What's circled in
green is Muse's hat, who was graphics staff a while ago.
What's circled in
blue is a hat Stella Bella made (along with multiple colors), who was graphics staff when I was hired.
What's circled in black is what I'm not sure if I've seen them on classic or not.
As for everything else, I'm pretty sure I've seen them on classic.
This isn't the only case of era taking hats from classic. When I was the graphics administrator, there was more than one case of staff telling me something they made was sold on era without their permission. It kind of annoys me, and by "kind of" I mean "extremely", but I know nothing will ever be done about it.