Thanks. I have upgraded twice since 4. That would disqualify me then. They let you go through the whole purchase process without asking for your serial number. Glad I checked on here before spending the money.
You could only upgrade version 4 and get the discount once; you couldn't do it twice. Do you mean that after you did that, you then upgraded whatever new version that was to another new version? Each upgrade gives you a *NEW* serial number which can then be used for an upgrade discount. As long as you haven't used the serial number from your *CURRENT* version yet, it's still available to upgrade with.
Have you upgraded since your Pro 7 install? If not, then it seems like your Pro 7 serial number should qualify . . . unless someone else used it to upgrade and gave/sold it to you. This is okay, but it would disqualify you from the upgrade.
Check My Account/My Software and see what it says about upgrading. Try the link below. As soon as you click "add to cart" a box pops up and prompts you for your qualifying serial number: