Red Book Question

Now that I have added up all the recent dollar mintages for another thread, I have another question.
In the 2010 edition why are only 2007 and 2008 Sacagawea dollars footnoted as "not issued for circulation"?
In the 2011 edition, 2002 has the footnotea added. What about 2003-2006?
In the 2010 edition why are only 2007 and 2008 Sacagawea dollars footnoted as "not issued for circulation"?
In the 2011 edition, 2002 has the footnotea added. What about 2003-2006?
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