This is not normally required. All 9.x versions use the same key and when upgrading from one 9.x to another 9.x you are not prompted for registration detils (same for 10.x, 11.x etc.).
What did you upgrade from and to? Do you really experience this for every minor upgrade? If you do, please contact us at firstname.lastname@example.org. We will not discuss registration issues for registered customers in public.