You ask a great question. Your track record is frankly a better question. How can you go that long without a miss is remarkable. There are myriad things happening to produce a litter and for you to have the stars align each and every time is great. Lucky but great.
My suggestion, don't fret about it too much. Try ovulation timing with blood work and get her next heat.
No I did not progesterone test because I had them both at my fingertips and she has a track record. I normally don't progesterone test unless it is surgical or I have a long drive to get to the stud dog.
It will be interesting to see if she did ovulate--because she wasn't flagging or standing at all. Very strange!
I had one come in heat in mid August. She was bred 4 times in an 8 day period. No pups. She came back in heat Dec. 2. Surprise, surprise. On about day 5, I did a in house progesterone, which suggested she was almost ready to breed. Two days later, I did another progesterone which suggested she was ready. I bred her and at 3 weeks I could already tell she is pregnant.
I don't go by what did your male think, are the girls mounting her. The girl on girl thing seems to be very early in cycle. Have not in 20 years done a smear. Thought those were usless. Make your money count. Do a progesterone test. You have been lucky. With what it all cost these days I don't understand not doing a Prog test. JMHO
My other girls were mounting her from day one, but she wouldn't stand for them at all either. Used to seeing flagging, standing for the girls, then introduce the male.
I had no reason to run progesterone since it was going to be a natural breeding with a bitch who has a history. The tests are $100 a pop here, so not something I do on a whim.