A question about 6.2 release

[PowerMan]

Dear sir,

      My first language is not English, if I made some bad words or
expression, please forgive me.

      I have learned from your web site http://www.freebsd.org
that 6.2-stable is relased on 15 Jan, 2007.

     But why there is also 6.2-stable snapshots released in May 2007
and June 2007?

     Should all snapshots be released before a final release is released?
     Should no snapshots be released after a final release is released?

     I can't express myself very well, I wish you can understand me.
Thanks.