It's definitely have different chronolgy/timeline/storyline/story event chain/story event order from the guide --- If you don't want to forget, don't even remember PSN Account: Aeria33, at your service !
There's really only a couple places you can "stumble" into that will kick you around in a "You Are Not Supposed To Be Here" yet sort of way.
Anyway, Yaschas Massif is chapter 3A; Sunleth Waterscape is chapter 3B. You don't have to do them in any particular order, but somewhere down the line from 3B you will need something you obtain at the end of 3A's timeline in order to proceed. --- [An honorary Vassal of the Lord Laharl] The best rating is your own. I don't base my choice on other peoples views - Samus1
Eh, Kingdom Hearts only opens up levels when you've completed another as I recall. Mostly you can beat a level as soon as it's available, or it recommends the level you should be before exploring.
13-2 has a few rare cases where you might go from, say, a "level 2" location to a "level 10" loctation by activating the wrong gate. There's not really any indication before you actually arrive at the new area, though.