I was on Premarin a whole bunch of years ago. Got up to a "B" in less than 6-months and then quite taking anything estrogen-related for over 20 years while the B boobs stayed like they were only less sensitive. This was a medical intervention for male-pattern migraines which were cured in a very short time.
I recently (about a year ago now) went on progynova for my prostate, osteoporosis and bone problems and almost instantly shot up to a really full B and right now am going for a small C, but REALLY REALLY FULL!
The soreness in them right now likely means I'll get some more decent growth. I'm bubbling out of all my B+ bras. My mom was just a B. :O
Anecdotally - I cannot recommend my regimen - but it worked for me, but then again, I am not trying to pass.