As I mentioned when I originally published my preseason top 50 prospects on March 26, I will be updating the rankings on a monthly basis over the course of the 2012 season.
Considering that most minor leaguers have only received about 100 at-bats (some more, some less), it makes little sense to shuffle the rankings based on such a small sample.
While there are a few players whose performances have been so outstanding that it warranted a more favorable ranking, this is not a ranking of the top prospects this season—it is the same top 50 overall ranking with some minor adjustments.
There have also been several players that have officially gained rookie status after amassing 130 at-bats dating back to last season: Mike Trout (No. 3), Jesus Montero (No. 12) and Yonder Alonso (No. 48).
Also, there are a few prospects that fell out of the top 50 not because they aren’t playing well, per se, but rather as a result of others' strong performances.
Therefore, there are a few new faces appearing in the rankings, and as the season unfolds there will surely be many more.