Are you passing the value of $AgencyName to the next page as well? If you aren't, the page has no way of telling what it is and therefore has no way of addressing the variable.
Looking at it and the way you have the name set up dynamically, you may have to use a variable variable, but not sure (I stay away from them myself, a bit confusing...strike that, alot confusing).
Might be a bit less confusing to set the select name to something static, and pass the AgencyName as a hidden value. Then do the comparison on the next page.
Jim