Within each outpost, the information is always provided in order of importance, with critical info like locations of objectives and prisoners provided first.
However, the list is different for each outpost. Here's a practical example:
In the mission C2W, the main objective is in the Eastern Communications Post, to the northeast of the LZ. A secondary objective is to rescue two prisoners being held in Da Wiallo Kallai, to the northwest of the LZ. There is a guard post between the LZ and the Eastern Comms Post, and the two guards there will always give you the location of the two prisoners in Da Wiallo. However, if you head for Da Wiallo first, you'll encounter a different guard post, and none of the guards there will give you info about the prisoners.
It seems like this mission is designed this way because they expect new players, still early in the game, to head straight toward the objective and interrogate everyone they can. This would give those new players info about the secondary objective that they wouldn't otherwise have stumbled on.
In many later missions, it seems that interrogating a guard anywhere in the area will give you high-priority information. But in certain examples, such as C2W, the info is divided up so that only certain guards can give you critical info.
C2W also gives us another interesting example. There's a piece of information that's not normally very useful - the location of the main transmitters that the CP uses to communicate with other bases - which happens to be very useful in C2W, because you can take it out in order to finish the mission without destroying any of the antenna dishes on the roofs. The location of the transmitter is a piece of information that can be obtained through interrogation, but it's one of the last ones you'll get - resources, diamonds, vehicles, etc generally come out before the transmitter or power generator locations. In C2W, this hasn't changed, even though it's mission-critical. You'd have to interrogate most of the guards before they'd point out the transmitter.
So this is another point where the information is managed to guide the player through a certain path. The way you're instructed to complete the mission is by locating and destroying all three antenna dishes. The transmitter location isn't put higher in the list because that would introduce the player to the alternate solution in a way that might be a bit too easy.
This is just one example, and things are obviously different in every mission. In general, you can trust that mission-critical information (including prisoners, who are usually a secondary objective) will come out first.