Why Does the AFMS (Aircraft Flight Manual Supplement) Have Some Pages With "FAA NOT APPROVED"

The AV-30-C AFMS is still valid. The "NOT FAA APPROVED" marking simply indicates non-regulatory explanatory pages, not that the equipment or supplement lacks certification. The MFG is the certifying authority. 
 
It is normal and intentional in many AFMS for avionics like the AV-30-C to have the "NOT FAA APPROVED" because only certain sections of the AFMS require formal FAA approval. 
 
Those specific sections of an AFMS that are FAA-approved are Limitations, Normal Procedures, Emergency Procedures, Performance (if applicable).
Those sections must be reviewed and signed off by the FAA or an ODA unit. 
 
Informational sections that are not FAA approved would be System Descriptions, Operational Explanations, Database Descriptions, Display or Color Explanations, Menu Navigation, Troubleshooting Notes, ect. 
 
These pages may say "NOT FAA APPROVED" because they are guidance material, not regulatory operating instructions.