On the middle one they only check if you go backwards from the position of the key (I got it to work clockwise). If you continue on the intended path and then go back the clock won't go faster. You have to be fast though.
It’s non-transferable in the sense that it stays with the car, not the owner. If the owner buys a new car they have to buy the FSD package again. But the car they sell on the second hand market will keep the FSD package, unless they sell it back to Tesla. In that case Tesla usually disables it before putting it back on the market.
I work on my cars as a hobby (not a mechanic). All the brakepad sensors I’ve seen were only on one pad (usually the inner one, as that wears off first). As for your 2 and 3, there is simply not a chance that a bump will make a pad fall off, unless the whole brake system has major damage.
The explanation is usually the simplest, they forgot to install it.