Apparently there are two varieties of North Korea’s 500-won note dated 1998 (B319). The first one features fine lines in the clouds surrounding the palace on the front (above, top). On the second one, reportedly issued in 2002 or 2005, the fine lines of the clouds blur into a solid fog as they get closer to the palace (above, bottom). There are also slight differences in the clouds depicted on the back of the note, and it appears that the color of the square seal with star on the watermark area may also be different, though this may be due to variations in printing over time.
Courtesy of Rui Manuel Palhares.