I don't know. I haven't tried for the full 12 months because there are only some times that I want to use Prime. I think I have four accounts with different e-mail addresses* but same name, delivery address, credit card and phone number. When I really need something quickly I just find out which one hasn't had a Prime trial in the last 12 months and sign up, order, then cancel Prime. The trial then lasts for 30 days.
It can also be useful for the occasional "Prime-only-one-per-customer" items too, if you need more than one of them
* For "reasons" I have a few domains so they are all me@somedomain