I'm trying to figure out just what year my 820 frame is from. The serial number doesn't match anything on the Vintage Trek website and the dark green color was used several years. My wife has a similar 820 in the same color that appears newer. The only significant difference, except for the graphics, is that mine has a weird little noodle of a cable guide near the top of the seat tube where hers has a traditional cable guide on the top tube.
I'm tempted to upgrade to a newer hardtail, but frankly, I think the old Trek will take anything that I can (or should).