I thought as you did, for years, actually, but listening to some folks who have put this to the test is changing my mind. It seems that smaller females can safely lay clutches, and they do continue to grow to large sizes afterward, and lay larger clutches. It comes down to the body condition of the female (is she nice and round?), and genetics.
I had thought that laying a clutch would surely slow a female's growth rate, as she put all that energy into egg production, but no one is reporting that it does...and some are reporting the opposite.