To expand on this....
If I buy a License on Jan 1st 2016 and let it expire (don't pay the $40 on Jan 1st 2017) and decide say in 2020 that I want to upgrade to the latest version, Do I have to "Back pay" for 2017, 2018 and 2019? in order to gain access to the upgrades in 2020? Or would it be the one fee of $40 on Jan 1st 2020 for the year?