My suggestion is the following:
I think that Wargaming should definitely change it so that for missions like —Get Medal "Warrior" two times in 12 battles— , it resets the counter automatically after each battle until you achieve your first "Warrior".
Why? Imagine you do the first of your next 12 battles and do not get 6 or more kills. Why wouldn't you want an extra try? It would actually be the best to reset after every battle as long as you don't have a warrior medal, if you really want to do the mission, because why wouldn't you always want to have the most chances?
But… do you reset after every single battle? Of course not, because it would be very time consuming and annoying. But at the same time it's illogical to not reset.
Therefore, I think that Wargaming should make it so that it resets the counter for such missions after every battle, as long as you do not have at least once fulfilled the condition. It would make the whole thing much more comfortable and less of a pain.
Of course, resetting it only possible as long as no tank of that nation is in battle, so they could make it so that at a given point when there's no tank of that specific nation in a battle, it resets the counter.