Pretty sure that's exactly what Tennenbaum was doing. Rather than admit, "the test didn't produce a result," he'd just make it up. Asking for information about period cycles and intercourse sounds like he was using that information to try to guess, with no more accuracy than the mother could have done by herself. They weren't even collecting enough blood for an accurate test, if he even really ran them. I bet it comes down to a combination of greed and hubris.