COPO F & SO number on Flint seat tag from 1969 Biscayne

[chadk]

I removed this seat tag from under the front seat of my Flint built '69 Biscayne. I was wondering if anyone could tell me what F4085 in boxes 12 and 13 means. It is a bare bones car that was ordered with L72 427, M21, 4.10 rear, and tinted glass. The original owner is still alive and doesn't remember ordering anything that would require a special order.

Thanks