Specific order needed to unlock coop achievements?

[Abaddon106]

Hey!
I started the game in coop in perfect agent with a buddy. We did missions 0-3 (shows 3 stars for every mission).
Now i played with another guy and we started at mission 7. As i am missing missions 4-6 the stars DO NOT show at the missions we played since then. The other guy told me that the stars won´t show up but the game "remembers" which missions i have beaten and the achievement for beating the game in perfect agent will unlock when i finish the last 3 missions and i will unlock dark agent difficulty.

Can someone confirm this?
I am afraid that all the missions we did dont´t count for me...