N = NEF, K = built in 1994. I would go by the terminology used in the 2005 catalog or from the NEF/H&R web site, Walmart may be using old terminology, but the firearms they receive will be of current issue. You can look at Walmart's supplier's inventory which is Sports South, the link is in the FAQ. You can actually see what's in stock with a description of the firearm as well.
Tim