Drafting Players In The MLS

The DCCenters has a nice find on players in the MLS. As you may know, the league holds a draft each year for young players coming in to the league. In looking at the numbers, they found that 1/3 of the players drafted in the first 4 rounds never play a game for their club. I wonder how many of those that do, are around in the league after a year. Or how many of them are still in the league playing 3 years later.