The GAF score is part of Axis Five diagnosis. It's an overall indicator of your psychosocial functioning.

The DSM details Five Axis of Diagnosis. I won't get into details, I find them pretty silly and it's not required to use the Axis Diagnosis system.

The ICD-9 code is required by insurance and medical authorities. Any mental health provider must use them as part of an indentifiable system.

Most psychologists I know do not think in the form of the DSM. It's merely a requirement they consult after speaking with the patient.

I don't know anyone except for billing coders that memorize the ICD-9 code!