I think those are standard across the player base. There are other specials that pop up now and then that are specific and I haven’t seen a pattern to those yet.
Re: Calendar offers - so far every seasonal event has had calendar offers I think. The bunnies last year was my first, I had only been playing a week or so, so I maybe mistaken on that one because I didn’t know what was what back then 
Edit: This would imply that there is a 15 day calendar offer: 🌿 Memento seasonal event