Is this the kind of summary data you're looking for?
The original spreadsheet(s) are too large to upload here.
If you need data further back or different just let me know and I'll get you what I've got.
"New teams" include both rookies and those that FIRST doesn't consider rookies, but are newly formed teams none the less.
P.S.
See if this summary that
DarkJedi613 produced last year is of any use.
It's a page with # of rookies for each year and retention rates. The row is the year you're looking at (i.e. the row 2006 refers to the 2006 season). Then each column is the number of teams (out of the original # of teams) that participated in that season. So for row 2006, column 2000: then 271 of the 372 teams from the 2000 season also participated in the 2006 season for a rentention rate of 72.849%.
http://www.team358.org/files/team_lo..._teams.php.htm