It's the version from when you paid your annual subscription (or 12 monthly payments ago) plus any bugfixes.
So you buy 4.3.2 and you will always have access to 4.3.Z
2 months later they release 5.0.0. Your subscription let's you use 5.0.0. If you cancel your subscription then can go back to your perpetual version 4.3.Z
At least that's how it's supposed to work
Given the timing i suspect this was the article that drove the change. It was shared quite a bit over past few weeks.