The Model number Usually starts with the number "20-" Followed by three numbers for the USA & Canadian Market
However the European and Australian market have the same number, but has the number "9" inserted before the first of the three numbers following the hyphen
Sometimes the number can have an extra zero before the hyphen and another immediately after
(20-173) can also be listed as (200-0173)
I hope that makes things a little bit easier to understand
Note: The Catalog Number displayed is the USA Catalog/Model Number.