restoring knotty pine wall panels

During this rainy season, I noticed that the pine wall panels in the bedroom were moist and damp. There are also dark stains between some of the panels, possibly from moisture and humidity. Some areas on the wall seem darker than others. This house is over 30 years old, but not sure when the panels were put in.

I want to restore the wall panels but I need help determining what color stain(if any was used) and finish was used . I read that back in the 1950's the knotty pine color was usually obtained by using amber shellac as a wood sealer, and over coating with clear varnish for durability. Could this be it?

I tested with laquer thinner and it seemed to have removed the finish. I also stripped down and sanded a very small area that was painted white. The color of the stripped down pine looks different from the one I used the laquer thinner on, giving me the impression that some staining was involved.