As some of you may know i have recently had a litter from Tilly (who was tested as Probably Affected) - she was of course mated to a clear dog (tested clear twice), only after discussion with lots of respected breeders throughout the world, and with our vet, we decided that to mate her was safe as she had no indication of developing Fanconi, and as she was only 2, very unlikely that any syptoms would manifest (though i understand not absolutely impossible).
She had 9 (yes 9) healthy puppies on December14th - reared them all herself, absolutely trouble free whelping, and all are now about to go to their new homes this week. She has almost got her figure back in time for Crufts next month, and she will be spayed before her next season. I respect the opinions of those who say they wouldnt mate an affected bitch, but all circumstances in each case have to be taken into account, and in our case i was happy that i was not endangering Tilly herself, and all pups should be unaffected as they will be Carriers - all being tested before they leave for new homes anyway.
I certainly wouldnt have considered waiting till her next season, as the risk would have been greater.