Good point, they really should be on the calendar. I guess they are meant to be like surprises, but they could show even if they get there only a couple sim days in advance.
I think there are several areas where the Season EP is not thoroughly integrated with other EPs. Like electronics breaking in the rain (Windenburg outdoors parties + the tech festival in San Myshuno. And there are systems (ie the club icons) that could be better updated to reflect the new features. The weather forecast TV could have shown the prognoses fo the other worlds. Needing to travel there to check the weather seems a tad tedious. I also find it strange that no wal hanging calendars were added with the Seasons EP, I still only have the cat&dog calendar from Cats and dogs ep, plus the Sims in uniform calendar from GTW.
Perhaps we like the calendar feature better than they expected?