Hi David - when you're examining antique gold hallmarks, it's a good feeling to see a crown before the 22 purity mark! Congrats! A starting point in a determination and a nice one at that. You know the ring dates prior to 1975 at least.
The O is the date letter. Even from the image, which isn't very clear, it looks like the ring has been re-sized. The jewelry repair could have interfered with the hallmarks.
The only think I can think of is that the "P" you see, was one of the letters of the maker's mark. It suggests a pretty iffy finger ring re-sizing job and could affect the value.
This is one of the reasons why it's so important, that if you need to get antique jewelry repaired, or change the ring sizes, to go to a jeweler who specializes in repairing Antique Jewelry.
