Harry Potter book first print question

[Chris]

I am trying to collect all the US first edition Harry Potter books. I 
found a site www.firsteditionpoints.com that explains what to look 
for to make sure they are in fact first editions.  I am confused as 
to what a particular # means.
 
Ex.  HP and the Deathly Hollows    (copyright page)  The web site say 
it should read as follows
 
                        10 9 8 7 6 5 4 3 2 1 07 08 09 10 11
                             Printed in the USA, 12<-------------
                             First Edition, July 2007
 
I have looked through several of these books and the # after Printed 
in the USA does not always match (several books have had 23,58).   
Everything else down to what the dust jacket is suppose to say 
matches.
 
I would appreciate if you could shed some light on the meaning of 
that particular #, and whether it makes a difference in determining 
if the book is first edition or not.

Any help would be greatly appreciated,
e-mail txohsobad at yahoo.com
Christopher