My main playthrough only has 92% for the 5th mission but missions 1-4 are all > 95%. Score Attack has one > 95% - looks like Score Attack doesn't unlock the achievement. I will go back and try to do this on a main run and see if it unlocks.
As others have indicated the final mission is a pain and after doing it 3 times I'm still 3% below what is needed. Oh well they don't call them achievements for nothing.