My understanding of it not being done in the past, apart from the possible mismarked puppies is that FN was a problem in parti-colours but not in the solids.
That's interesting as Muffin, solid black show type, is an FN carrier. As her pedigree contains well known show kennels I would of thought that there would not have been parti-colours mixed in as they were being bred for showing.
However lots of owners of solid show cockers always ask how i got his coat to be so soft, so now im wondering i the parti colouring has caused it to be so much softer than some of the solid cockers you see.
Muffin also has a very soft coat, but that might be because she has been spayed.