This isn't what's happening. Anyone who subscribes to FSD has access to current capability features. Like most software services, there are no refunds for software purchased during a billing period.
If not presumably they could argue that they never received what they subscribed to.
There's a separate $6,000 "Enhanced Autopilot" upgrade option that covers the first five features ("Navigate on Autopilot" ... "Smart Summon").
That's all the detail I get. I presume that at least auto park and summon are unlocked immediately, because those worked on my previous leased Model S without being in a beta. The the first feature "Navigate on Autopilot", which is in both options, sounds like has to be an over-sell. How that doesn't imply autosteering is beyond me.