In 2000, Leatherman Tools went on an absolute frenzy of new product introductions. They brought out the Crunch, Flair, Pulse and Sideclip early in the year, and then the Wave near year's end. Meanwhile, the 2000 version of the Leatherman PST saw a minor change near the end of the year. Early 2000 tools are the same as the from 1999 model, but late-year tools added a small nub to make it slightly easier to open the medium screwdriver, similar to the early 2001 PST.
Note that even with the nub, you still can't open the medium screwdriver by itself if you have typical fingernails. It is indented so deeply that you still must pull open either of the tools next to it, and then slide them apart. The nubless models are a bit sleeker, and less likely to accumulate crud.