I'm an ESET Anti-Virus Silver Partner, well actually not me personally but the company I work for although it has been through my hard work that we reached that status. All of the subscription based protection companies generally work on a one, two and three year renewal service (Some do five years and more). The other day I was working my way through some renewals and a customer renewed for two years. About an hour later I had an email from the customers accounts department.
✉ Accounts: "Hi, you've just sent us an invoice for our ESET Two Year renewal. Can you tell me the date it starts from and the next date of renewal?"
⛹ Me: "Umm? Well as you can see we renewed today so instead of 2017 it will be 2019 for the renewal."
Well Duh!

Pete