Alan, I'm sure the referral ID just gets stored to the session after the initial click. I doubt you need to add it to any subsequent URLs.
Edit: And in case you are interested in the technical explanation: A lot of web sites, and probably most e-commerce web sites, keep track of your session using cookies. Often there will be an encrypted session variable which will either contain encrypted data, or more likely, an encrypted ID which is used server-side. The encryped ID might point to a row in a sessions table in a database. So, in one possible scenario, when you first visit the powells.com, it creates an entry in a session table on a database with an ID #, and associates it with your pid #, along with other information. The session id # is encrypted and stored as a cookie inside your browser. As long as you don't close your browser, the session will persist, and it will know your original pid # as you click around the site.
Last edited by Martell; 09-16-2009 at 10:06 AM.