Its a good question Trojan.
If a good pairing has been made up from some years ago from well known hunting blood lines, or birds that have proved themselves in the field time and time again then I can't see it making much difference to the quality of the youngsters however long the pairs have been grounded for breeding! the blood line will still be the same while that pairing are together no matter what....
There's a few things that give me the arse! for instance when related blood lines are placed together for so called line breeding or perhaps because both birds was good performers i