For the, "next guy" they can tell when the PCM was written with a timestamp. Purchase date would resolve that. The dealer is then responsible for determining if the tune caused the problem. Ford only looks that deep into it if they have to (per my dealer). So a blown motor with symptoms of being run lean or too hot may prompt review of the PCM. A leaking exhaust gasket or bad rear-end probably will not.
There is probably a way to wipe history. But I have no clue how you or I could do it without it showing the last time it was written. And if it shows it as being any date other than date of manufacture or a date that the dealer needed to access it, same boat.