Forum Search is missing a lot of my old threads?
 

It looks like when I moved from 3.8.5 to 4, my search is missing lots of pertinent data (like everything from 2005 through 2009)? Do I need to rebuild the search index? Forum has 800K posts...sounds like this will bring a lot of servers to a halt :( New threads are being shown...so are 2004 threads and older.

:confused:

Thanks for any advice.