Yawn. I a little while ago I signed up on some Xbox site and got THREE full subscriptions to CGW, XBN, and EGM. I know it worked, because I now have 2 issues each of XBN and EGM and 3 issues of CGW.
I sign all my free magazines with the exact name, address, email address, etc. It seems to work every time. I check the magazine subscription status from the Ziff Davis customer service website just to see if the subscription goes through. If they do give you duplicates, just send them an email stating you're receiving duplicates and that you should have received another year to your subscription