The way I understand it... sort of!
Typically premium and regular are blended together to create midgrade. In Minnesota, we usually have 87-89-91, so 50 percent of each 87 and 91 make 89. Gas stations don't buy midgrade, they blend it. So your Shell 89 would be part V-power nitro and part standard top tier Shell gas. Of course, I could be wrong but as I understand it, that's what happens, but it could be different for Shell. They don't advertise V-power Nitro in the 87 or 89 because they want you to buy the premium, and the midgrade is (at least here) half premium and half regular.