Obviously, I'm reporting second hand for my wife!
We use Billings, baby exclusively nursed from mom for 6 months (nursing went on another 6 months with minor baby food supplement), but babies slept in own room / crib, generally waking to eat 1-2 times per night (don't miss THAT, but wife couldn't sleep at all with baby in the room).
Absolutely no mucus present at all for 4 months, then it appeared again just before peak time. The next 3-4 cycles were MUCH longer than normal, but things settled down again after that. It was weird and seemed unpredictable at the time, but in hindsight, the mucus was a highly reliable symptom to watch for. For us.
I'm still convinced that this method requires refraining from mucus affective cold medicines too, but I have no medical data to back up that personal opinion. My wife never liked those meds anyways, so no issues for us.