It was a fiction.
The technology to match traits & skills to dna is fictional.
Which means that the entire DNA map provided with each sale was fictional.
All their babies come form the same 15 kidnapped women, of course the Doctor's will lie about how difficult it was to find the magic babies with the specific DNA that is tailored to the customers needs.
The many women they had on the production line guaranteed eye colour and hair colour, and body type, but after that, it's impossible to double check with just your eye balls.