Understood. That's somewhat annoying. I have 4 computers in my household and I wanted all of them to have OD. That means I need 4 unique email addresses to buy and maintain 4 licenses. I feel for people who have a small business or a larger number of computers.
I ended up buying it at regular price because it wouldn't let me get the upgrade price because I was already a licensee. The "new purchase" process doesn't run the validation check against my email address so it doesn't know I already have a license.
However, I now have 2 OD serial numbers associated with my email address. I'm not sure how that's going to work out long term.
Looks like an area for improvement.