This is a subject of great interest to me, as I'm in the same boat.
What worries me is this: Is this an "advance" on what I'd have, anyway, so I'm not really likely to develop much more, or is it rather a "bonus", above and beyond what I'd normally get?
Essentially, imagine my future boobs are rated 10 on an arbitrary scale - does this mean I'm already at stage, say, 5, and therefore only have half as much left, or that I'm at 5 but the end has been raised to 15? (Numbers don't mean anything particular - just there to make my point more clear.)