Breast growth comes in spurts. I am coming up on two years on HRT, and I have been having a growth spurt for the last couple of months.
My growth spurts do not result in an increase in my bust measurement. I was 39.5" before I started, and I am still 39.5", so any outward growth of breast tissue has been matched by loss of muscle and fat. But I do feel the breast tissue growing wider and more solid. For a long time, I didn't quite fill an A cup. Now, I fill it. (Yay!!) Given the genetics on both sides of my family, I don't have much hope of reaching a B.
But I am happy because they are mine, they are real, and they are as cute as the dickens!