IntelliJ uses this model too.
https://sales.jetbrains.com/hc/en-gb/articles/207240845-What...
"When purchasing an annual subscription, you will immediately get a perpetual fallback license for the exact version available at the time (of the purchase)."
Parenthesis mine.
You buy version A (for full price) They upgrade you to version B (hoping you will pay the reduced price) When version C come out if you haven't paid yet you get reverted to version A