Just a handy little tip: In salaheem's sentinels, check the first npc that walks in and talk about merc assessment. My friend with 3 wins has his saying he's pulled himself up between the borderline of worthless beaten pulp and respectable employee
I have 5 wins, mine says: A few more successful missions and the preseident herself might have a word with you. Keep this up and the next mercenary rank is not far off!
This leads me to believe that it's based off either total wins or winning all areas (i have 4 total beaten, 1 repeat, he has 3 total beaten)
Anyway thought it's a nice little thing I saw that nobody else has mentioned as of yet, so there is hope of more assault missions without waiting on next patch