remington model 31 marking info.

[kcie]

I have a Remington model 31 with a 30 inch barrel 12g full choke. Barrel markings show that it is a May 1948 (KL). Serial number is 58201. There is a marking on the bottom of the receiver I.O.P. P-48. I would like to know what distinction is that marking. Thanks

[rossew9362+31]

Looks like KL is May 1942 to me. I am watching for the reply of the under bbl number as I also want to know.