Bryan Litz seems to test a lot of bullets BCs against manufacturers data. Absent being able to test them yourself, who would think has the more accurate data?
Bryan's ballistic app shows his calculations. Some are considerably different in either direction. For example, Nosler gives the 200 grain 338 Accubond and BC of .417 but Bryan tested it at .461. Nolser gives the 120 7mm Ballistic Tip a .417 but Bryan gives it a .365.
Actually works in my favor for my 338 Federal. Both the 180 Accubond and 200 Accubond showed materially higher with Litz's data which was the exception for Nosler. They were almost all overstated as a brand.