Small Follicle, positive OPK, BBT shift

Hi Ladies,
I had a small follicle, as seen on my ultrasound on the day of a strongly positive OPK. My Gyn said, it is too small and may not have a mature egg. Nevertheless I saw a clear temperature shift on my chart in 2 days, indicating ovulation.
I've been charting sincerely for 12 cycles now and have been regularly and naturally ovulating (mostly somewhere between CD17-CD27), always confirmed with positive OPKs, fertile CM and followed by clear BBT shifts.
My question is, does that mean I am releasing immature eggs every cycle, or rather, can I get a BBT shift even in absence of a "properly matured" egg release? Anybody can share their experiences on this please???
I thought my ovulation was not an issue based on my charting so far, but this ultrasound is making me doubt everything that I think about my body
Thanks for any comments!! Wish u all the best