The cost for the part at the factory for 1,000+ units is radically different than the part for your one off garage build.
Many years ago I was servicing Maserati GranTurismos and Quattroportes of which some use a ZF 6 speed auto transmission. Since the same transmission is used in Land Rovers, I would buy parts from the Land Rover dealer which was nearby. One time I went there and they didn't have any fluid for the transmission for Land Rovers, but they did for Jaguar. The fluid was identical, but on a different shelf, and cost a lot more. The parts department said that Jaguar uses a 3rd party parts distribution contract in North America, but Land Rover does it in house, so every Jaguar part, of which many are identical to Land Rovers, costs more. They could not just bill out a Land Rover part internally to their own dealer to service a Jaguar either (they were a franchise that repaired both).
Typically nobody would actually go through with placing any orders beyond that point, unless they’re the pentagon.
I don’t think anyone suggested manufacturers could get away with lying all the time.
my company has looked into spending billions for a chip fad of obsolete processes just to get some no longer in prodction parts. So far not worth it.
Businesses previously and will continue to negate it in practice, sometimes for legitimate reasons and sometimes not. And most of the time nobody outside of a small group will know for sure.