I'm not saying you missed testing, I'm saying that it's entirely possible that the hormone, while detected by your body and it signalled you to ovulate, did not get in your pee in a high enough concentration to register on the tests. So you could have actually had a positive more like CD 14 or 15 and it was just in the early stages and didn't show on the OPK strip, but your body still "heard" it and it triggered ovulation.

The LH is like a message. Your body can "hear" it at a whisper and even if it starts "shouting" later on, it was that first "whisper" that sent the message. That is why we go off the first positive and NOT the darkest, because your body can hear the "whisper" and does not need the "shout."