My current unpopular opinion is people sulking about the events and wanting this years DIYs to still be available next year. I'd be bored if they released the same ones next year. (I actually dont have half of them because I started my current file on september 1st, so I'm not saying this because I safely have all of them).
I think the idea of retiring certain event DIYS makes it more fun and gives them a certain value? If you missed out on this year, you missed out on this year, there will be new ones to collect next year.
I think they had limited edition items in New Leaf through the post office (some kind of zodiac item maybe? Cannot remember). I wasnt crying unfair when I missed out on those. I thought limited items were a fun idea.
My understanding was that no DIYs have been removed from the game. You can just time travel to the event you missed (forward or backwards) and get everything.
That isn't to say that most players play that way, but I'm not aware of any inherent exclusivity to any of the items. Maybe the patch download rewards, maybe?