I've been fighting with Tesla about this issue today, to no avail. I bought a 2017 Model S, registered on 28 March 2017; purchase from a secondhand dealer who advertised it as FUSC. The charging screen says "no recent supercharging" -- indicating the car did have FUSC with the previous owner (in line with
this). The "details" screen however now says "pay-per-use supercharging".
The discussion with the Tesla agent today was super revealing. He said that FUSC gets cancelled when the current owner "removes" the car from his/her Tesla account, e.g. when selling it to a secondhand dealer. This is of course what happens for SC05 cars -- but he said it also happens to SC01 cars (the code where FUSC is meant to be "for life of the car"). The only way to retain FUSC is to do what the OP of this thread describes: transfer the Tesla account, rather than removing it from one account and claiming ownership via another.
It does seem to me that Tesla are undermining the value of cars sold with FUSC "for life of the car". Given what the Tesla agent told me today (and assuming it is true), no secondhand dealer should be selling a car with the assertion that FUSC is transferable.
It's not clear to me what recourse I have here...