Nothing is 100% in this hobby. I have a pair of tomato clowns that have been together since they were at the lfs (I've had them for 6 mths) and they still havent mated. Although one has turned into a female and turned darker and larger then the other.
Nope...I have a pair of false percs that I've had for a few months...and the previous owner had for years (at least 3+) and they have never mated. My maroon pair as well that I've had for many months also hasn't done anything (but the male is MUCH younger so they might not even be close to thinking about it).