
To be honest because of how seasons may fall most people who think of two as a MINIMUM age will not mate their bitch until later than that.
I have mated a bitch who whelped 5 days after her second birthday, left a season between and tried again for a litter 16 months later and she missed. Now waiting for her to come in season and if she takes the litter will be more than two years since the first. this bitch has longer than a average inter season intervals , so in breeds where 8 - 12 months seasons are more the norm a breeder might choose to breed a bitch at just two rather than wait, for whatever reason, but generally there should be no great hurry, certainly not to have another litter quite so soon after a large litter.
The main issues with this set of breedings is the lack of health testing and repeating the mating, which is never a good idea as it adds nothing new to the gene pool. A repeat mating could be justified if the first litter were small and the quality wasn't in the sex you hoped for, but one would think with a large litter before there would have been something suitable of the right sex to keep, if not then repeating the mating is pointless if quality wasn't there.