For the record, USP or EP and food-grade(fcc), are often the same high standards, but sometimes they differ, and so to be absolutely sure of getting the purest "mainstream" product, then we use pharma-grade(USP and/or EP) whenever the product has a monograph available in said compendiums. PG and VG has monographs, so we go for USP/EP there of course. Btw, many shops and ebay/amazon dealers lists food-grade, because that's appeals more to the public, as the consumers not using it for ecigs don't know what USP means. A product can easily be both USP and food-grade.
Lastly, some state food-grade, because well, it is food-grade, but also because they
buy big drums of USP VG/PG and then when they open and distribute into smaller bottles, then I don't know for a fact, because couldn't find proper evidence, but likely is correct, but they state that they need an iso-8 cleanroom for the redistributing or else they "break" the USP grade specs... Many of the VG's we use are like that, but as long as reputable seller then I trust them fine. Also, if going 100% by the USP spec, then not in the main monograph for glycerin but in the beginning chapters of the general USP articles they state that the product is to be listed 'Glycerin USP' on the label(monograph-name USP) and no other combinations i.e. 'VG' or 'Vegetal Glycerin 99.7% USP", which is very rarely the case for what we buy, but it's properly like that in the original drums the resellers buy...
Also, USP/EP isn't meaning OK for inhalation, and all the VG's we use doesn't list inhalation as OK in the MSDS's, but as it's a pretty pure product(99%+, and usually 99.8 for USP VG) and there's decades of tests done for inhaling PG/VG, then it's considered fine to do anyway. To be "inhaling-certified" the manufacturer need an additional license in addition to being USP grade...
Edit: bwh79, I fully understand what you mean, and it seems logical, but i'm not 100% sure we can always say that. There could be very slight differences, where the food-grade monograph has a substance listed for test that isn't mentioned in the USP. I agree that would be odd. Anyway, the most proper answer to why that isn't always so, is that to be able to say food-grade, you have to specifically test against said monograph, like with USP. If you haven't, you cannot state food-grade, even though it would pass most likely always. I have seen a bunch(50+) COA and MSDSs etc, and sometimes they state USP and/or EP, + e.g. E422/FCC, and other-times not, but that just goes to show if the manufacturer bothered to test against the food-grade monograph. If they don't market for food, then they sometimes don't bother.. In general terms, we can probably say that USP = food-grade, but not always other way around...