The answer is "maybe". With time and feeding, they may grow to that size range. Or they may not.
Is it worth it to you to wait and see? Is a 7 foot snake worthless to you?
Its pretty disturbing to see that you appear to be focused on the size of the animal to the detriment of everything else.
I do have to say, this is true, it might get there at a slow rate, or it might not.. In the long run do you seriously love your snake less if it's not 9ft? Because if so, should you even have the pet to begin with??