My grandfather was involved in an investigation for Leyland trucks where vehicles sent to South Africa kept dying with all the apparent symptoms of low oil but the people over there swore that they were putting the right amount of oil in at the specified service intervals. On going out there to physically watch them it turned out that their standard size of oil bottles left about half a pint of oil over when the engine had the right amount in and their standard practice was just to throw the extra little bit in. This little extra brought the level in the sump up enough to have the big ends dip into the surface of the oil when the engine was running and it whipped the oil into a froth that the oil pump couldn't suck up - cue dead engines due to oil starvation despite having "plenty" of oil in them.