You can stack up to 10 times that’s 50 sites in total. After you register with the first code, rest you will go for an upgrade till stack 9 listed in your account.
After you use all the discount codes from AppSumo, You can stack additional 50 sites from https://analytify.io/your-account/ for $299, You can pay via PayPal or Stripe, that will be 100 sites in total.