It's probably multiple bugs in play, on top of the one where quests don't seem to update correctly as far as the death of something or a group no longer harassing someone/someplace.
I actually tried to take care of an army on the march (well, it was a dwarven one and I was trying to reset it), but they still respawned, even after using DFhack to give everybody a lava bath.
It'd be great if Toady One fixed the sleeping army 'problem' (quasi-bug quasi-unfinished-feature). It's possible to stop them sleeping by putting [NO_SLEEP] on the four main races (you could put them on kobolds as well, but it's rarer to see them in 'sleeping beauty army' form, though there isn't a whole lot of interaction and they just stand around, with occasional patrols.
Armies on the march are also apparently composed of civillians.
What do you do if you meet a GCS as your first opponent and you have a steel helm?
Pray to sweet Armok doughter... say goodbye to your god and... Meet your destiny!
If it will spot you, you are dead, because it will no tire, so it will overrun you if you are not cursed and will be biting you as long, as it will bite by helmet to your sweet flesh.
You can still outrun it, just don't get caught in any webs.
I got lucky once though when my loaded down adventurer was being trailed by a giant toad (or maybe giant olm) when a GCS ambushed me, but went straight for the giant toad instead of me.
Question of my own, how do I get my dwarven adventurer to go into martial trance? I've never had one go into that before.