The 2001 NLCD. For the 2001 data, USGS used different classification algorithms in different areas which were 'tweaked' to give more accurate results in each region; I think the value was 70, or 80 %, but was not able to find the reference yesterday.
Refer to the article you provided the link for. In the data set provide, each of the classification catagories is assigned and displayed with a specific RGB value. Three years ago when I check using Photoshop, I found some of the values differed by a number or two (from the values given on a USGS site); however they were consistent.