That's what one would naturally assume. But it always gets debunked (usually by me). Back during Covid, there would be a wild rumor of "they're out of pano sunroofs", or "they ran out of g/t exhaust systems" or whatever. And every time, I would pull up the day's build sheets and show dozens or hundreds of trucks that had that exact part on them.
There have truly been a handful of times when they actually ran out of certain parts. And it almost always caused the rest of the shifts to be cancelled for the day.