Correction! In the QA, I said that Wal-mart had made the mistake about the pregnant mom, but it was Target. We regret the error. https://www.forbes.com/sites/kashmirhill/2012/02/16/how-target-figured-out-a-teen-girl-was-pregnant-before-her-father-did/#468d313b6668
Correction to the correction! It might have been an urban myth!
Correction to the correction to the correction: I check with Charles Duhigg who wrote the original Times article and he has confirmed the story with several people. Myth, busted.