I would guess there have been some little changes in the "mil-spec" over the years, I really can't keep up on all the stuff.
Mine was made in 2002...the year is marked on the frame under one of the grip panels, it has the lowered port, but is not reflected in the serial number at all. I do notice that they are all marked lately in the boxes as "GI" although some are actually mil-specs with the three dot sights, at some point they may have added the white dots to the higher sights, beats me. Some of the older SA's also have a frame that is slightly "blocky" looking or more "square" looking, at some point they changed that as well. Not sure when that happened, but they slightly changed the frame shape a little bit at some point. Now I notice newer mil-specs have stainless barrels and stainless barrel bushings, mine did not have that.