Germinoma Bone Age

My son is almost 10 years old. He was diagnosed with Germinoma 2 years ago. At that time he had a growth burst and  Precautious Puberty and his bone age was 11.5 in Oct. 2006.

He completed his treatment Aug last year.He had a bone age scan 7 months ago and it was 9.5 years old.  He just had bone scan again 2 days ago and we were told it was 12 years old.

I was shocked by those results. I am just wondering how bone age was read. Why is it so different? He is shorter than average of his age. We will start his GH soon but still have some concerns.

Is there any ddoctor you could recommend to us? We live close to Atlanta and do not mind go to vanderbilt.

Thank you so much!!