Noticed that upgrading "Additional mercenaries" has no effect on currently owned mercenary camps. I was expecting to see the amount of mercenaries increasing, however they stayed the same.
Not sure how the upgrade affects unconquered mercenary camps. If the amount of mercenaries is calculated at the beginning of a map, then the upgrade should be done after winning a level, before starting the next.
Anyone tested that?
And anyone noticed if the Mercenary Discount upgrade affects currently owned camps? I think it does, since the tech affects them, but haven't tested it yet.

That's an interesting question, but I have to say, I would never notice this. I upgrade my advancements immediately after starting the next level and at that point I hardly have anything that would show actual number changes. So, it this proves right and isn't just a bug, I might start doing my advancements before starting the next level, but I don't save any APs to spend them halfway through the level anyways.

The advancement applies when you conquer the camp.

Thanks, Fizzer, for the clarification.
This means that spending AP on Additional Mercenaries at the beginning of a level is effective through that level.