There are dishonest people who make their living by scamming unsuspecting customers. It's easier to do when there are less (or no) regulators to ensure customers are getting the genuine article. There is more potential for it with high end luxury products because there is more profit involved. Because quite a bit if money can be made counterfeiting, counterfeiters will sometimes make the investment to produce perfect duplicate labels and containers. Unfortunately a sad fact of life.
That said, what we don't know is the entire history of the engine in question. Is it possible that before you used M1 0W-40 you (or the previous owner) used a lesser grade of motor oil, especially a conventional in excessively hot desert conditions? A less probable theory would seem like: for the period of time that lesser oil was in use, it made deposits in the engine, and now, after changing to M1 0W-40 synthetic, those deposits were loosened by the previous three fills and are now (finally) freed up and circulating with the current fill. So if that's the case, it could be possible you received genuine M1 0W-40 every time.
But it just seems more likely that the 1st or 2nd fill of M1 0W-40 would have performed a significant amount of cleaning on the existing deposits and the results would have shown what you are seeing now on the dipstick.