The first letter is a "1" which stands for Feb and the P represents 1967. So, your gun was made in Feb. 1967. "12" is the Assembler's stamp.
For further reading, I suggest John Lacy's book, The Remington 700: A History and Users Manual. It's an excellant book which should be updated (printed 1987).
[This message has been edited by 4V50 Gary (edited October 19, 2000).]