To illustrate my point about development continuing for a number of years here is a look at my development over the last 3 years using the same bikini top...

The top left picture was taken at the end of March 2015 after I had just started HRT.
The top right picture was taken a couple of days ago.
The bottom left is the day before I had BA about 6 months after the top left picture (Aug 2015).
The bottom center is a few days post BA surgery (Sept 2015).
The bottom left is April 2016 which was a little over a year on HRT and 7 months post BA.
Even three years after starting HRT mine are still changing and filling out. Puberty takes 3-5 years to happen and when we transition we go through puberty again. While most of the major development occurs in the first 2-3 years, the changes continue to occur for a few years after that. Throw in something like getting GCS and a whole new dynamic occurs. I know that I experienced changes in by breasts post GRS and I've read the accounts of countless others who had the same experience.
I am glad that I didn't wait 2-3 years to have my BA. I consulted with my therapist and my doctor who all indicated to me that there was no real need to wait that long to have the procedure, but then again I didn't go particularly large for my size.