This question could be applicable to almost any prop that goes up for auction, which wasn't specifically "gifted" to someone who worked on the film by GL.
This is overall a flawed example with a car sale, as title has to be legally transferred for ownership/registration/ tax purposes, but hear me out...
Let's say that back in the day, I purchased a brand new 1976 Ford Mustang with my own money. I drive it for a few years, then leave it parked in my parents' backyard work shed while I go college, fall in love, get married, start a career, have kids, etc. I never drive the car again. Decades later I see the car up for sale at a national auto auction company (same VIN, so I know it's the one I purchased), being sold by someone I don't know, and never heard of.
The guy says he bought the car from a another guy who owned it for 20 years before he did. The guy has never heard of me, either. I call my parents to ask what happened; they never told me they got rid of my car, I just assumed it was still in their backyard shed. My parents tell me that they paid some dude years ago to clean out the shed and do some maintenance work, and they told him to take whatever he wanted. They though the car was useless to me at that point and they didn't even think to mention it. So he must have taken the Mustang (the keys were above the visor) with him. But there was NO transfer of title...
1) Don't I legally still own the car? Even if my parents told someone to take it, legally they had no right to do that (assuming that state law may/may not allow them to take ownership if I leave it on their property for X amount of time, etc).
2) Ignoring that in the real world the auction house would not even try to sell a car without clear title... couldn't I stop the auto auction?
3) If the statute of limitations was not expired, could I file a police report against the guy who took the car from my parents' shed?
Another quick example: if someone breaks into my office and steals a computer, then sells it to a pawn shop, and some innocent guy buys it, THEN the police track my computer down: In the U.S., as the property is stolen from me and I can show ownership, then I get the laptop back and the innocent guy who purchased it from the pawn shop is just out of his $$, correct?
Why wouldn't LFL speak up and stop these auctions? There are MULTIPLE screen used props listed on the Heritage Auction site.