Which is why I mentioned earlier that I don't have a "favorite" manual--or Internet source. I consult them all--partly because powders can change considerably over time, despite retaining the "manufacturer's" (often a distributor's) designation. Often the newer versions are even made in factories on the other side of the world from the original factory.
Yet I still know handloaders who believe some manual is the best because they "agree" with it. Many still have major flaws, some which I've mentioned already--such as pressure-testing in one barrel and then chronographing the same loads in another barrel.
Then there's the difference in pressures that various bullets create. Yet some handloaders still believe that, say, all 180-grain .30 caliber bullets result in the same pressure with the same powder charges--not to mention differences in brass, primers, etc. This is another major difference from older manuals, which often lumped all .30-caliber 180-grain bullets into the same data. But even quick look at modern data, such as Hodgdon's Annual Manual's, shows significant differences in pressure with various .30 180s, when using the same powder.
