Did you buy your Mercedes from inventory? I believe you are over-thinking this. But I understand where you are coming from. Most people (including me) would prefer to see the car, on the dealer lot, check it out (maybe even think about it for a couple days and return), test drive it, and buy the car that day knowing exactly what you are buying. Tesla is not like this and probably something you have to get over because the people you will speak with generally have no idea what they are talking about. You think they are lying but the reality is they don't know and may even think they are correct.
FWIW, I bought a April 19 build "inventory" car in April (7 miles on odo). Nothing was finalized until I saw the car.