As said before, Jimmy's April Fool's intentionally reveal usually one, maybe two things that are happening for the event in some fashion. The rest of the things in the April Fool's videos are literally a April Fools joke.
Now as for his Cryptic Comments/Performances videos on the other hand. Those show he does have inside info as every cryptic video is connected to a house, scarezone and sometimes a secondary show like the RHPS. Once a house/scarezone is revealed by the event, Jimmy then posts a decryptic video how a cryptic comment (or in the case of this year and last year, perfomance) is connected to a particular attraction. He's been doing this for a while, and he's been spot on. As also mentioned, if there is a sudden last minute change etc. which has happened before, he takes out the corrosponding video and makes a new one for whatever is replacing it. (Prime examples being AWIL and the Chubacabra/Urban Legends house getting shelved in 2012 due to Silent Hill getting dropped on them and Comcast wanting Transformers RIGHT THE F NOW.)