NO pidyon is done if a male is born VBAC. I, too, learned the opposite in school, and was deeply embarrased when I had a boy VBAC and told my rov that we were planning a pidyon. Thus began my problem with seminary girls teaching halacha….
as far as the miscarriage – the mishna explains that if the fetus was “formed” it releases the parents from pidyon obligation. In recent years, it has become more and more possible for a woman to know that she is pregnant before 40 days (the mishna deadline, which btw is the day when gender is established hormonally), and thus that she’s having a miss. Previously, they probably thought she just had a late cycle. In any case, a miss before 40 days doesn’t count and a son born naturally after that is the recepient of a pidyon.