Swedish Place Names

I keep finding Swedish place names followed by a single capital letter in parentheses. Like: Lerum (P) It appears that the letter stands for a län (like a county). Göteborg och Bohuslän is (O), Älvsborgs Län (P), and Skaraborgs län (R).  The letters somehow correspond to a lettering system used for car license plate numbering.

A handy guide to old and new läns.

Here are the mostly relevant areas for my genealogy:

New Old Year Used Län (County) Landskap (Province)
(O) (O) (P) (R) 1998 Västra Götalands Län Dalsland, Bohuslän, Västergötland
--- (O) 1680-1998 Göteborgs och Bohuslän Bohuslän, V. Västergötland
--- (P) 1634-1998 Älvsborgs Län Dalsland, Västergötland
--- (R) 1634-1998 Skaraborgs Län NE. Västergötland