Hmm, interesting Irene. Let me offer this scenario: Let's say you breed over a 4 day period. Then let's say your female has her litter early, maybe 4-5 days before her should-be whelp date. Then the pups later conceived would have actually had 8-9 days less to develop than the normal gestation period calls for. What difference could it have made in this case when they had over a week less time vs only a day or two less time? Just interesting to think about.
BTW, thanks for your response!