They are intentionally not labeled as such, as at least a couple are supposed to be "surprises" (i.e. the second lance pops up and takes you by surprise, although obviously that only works the first time).
That said, reading the descriptions will often give you a hint (they'll mention multiple groups involved, or some other condition). Also note that some of them come in multiple flavors (e.g. the one where one of your pilots is babysitting a group of newbies can have several very different options for the opfor, depending on which flavor you get).
