The registration data just comes from the
FIRST website at:
http://www.usfirst.org/whatsgoingon.aspx
I have various filters I run it through to look at what's changing.
We also have kept records from earlier
FIRST team databases that have now vanished. The raw form of this data is at:
http://www.team358.org/files/team_lookup/
That database hasn't been updated in a year, because our webmaster has been in the middle of a database upgrade and got distracted by having to look for a real job after graduating college...
There are some errors in it from the original sources that we've been able to isolate and remove in the derived records published here:
http://www.team358.org/files/frc_records/index.php
To compare against past year's I just keep records when I do this every year. You can do this yourself just by looking back through older Registration threads.