The few cases I've read about ended with Tesla reinstating whatever the option was.
It makes it impossible to sell a car 'as-is' if the sale has to carry a rider that Tesla might change something after the sale regardless of there being a contract of sale with Tesla or not.
In the recent postings it's clearly up to the seller to be certain of any claims they make ahead of the sale. If it was sold as including FSD, then the seller should stand by that claim. However, if there is absoutely NO contract between a car owner and Tesla, then what would regulate Tesla's ability to make retrospective changes to vehicle specifications?
I haven't tracked cars passing through Tesla, but I understood that it was common knowledge that cars passing through Tesla could have soft features added or removed.
You are quite right to question if that systematically happens in practice, especially on cars originally sold new by Tesla including FSD. The problems seem to have cropped up when a review of spec is triggered by a change of ownership. In such cases it could be impossible to know for certain what chabges Tesla might feel entitled to make once a buyer takes ownership.