That's really weird on the not TTC if you O on day 16 or later! I assume it meant if you have a 28 day cycle and O on CD 16, as that gives you an 11 day LP...I have LP defect and it would vary between 10-15 days, took us two years to get a sticky pregnancy.
It is really weird PZ, I cant think what its called but there was an entire e-book written by an american woman based around not TTC if you O late. She claims that along with a lot of other stuff created her miracle children. Interesting but yes, a little odd