This is a perfect example of why every handloader should keep a veritable library of reloading manuals, both new and old. I have Lyman and Speer manuals going back to the mid-1960s, as well as current offerings. This way, I can average out the loads from several different sources and get a rough idea of the powder weights I will try. Perhaps the most useful info is the top velocity a load should achieve; then using my chronograph, I know that when I am approaching the top velocity, I am also getting close to the max load for my rifle.
In the OP's first photo, note that Hornady lists loads for both W760 and H414. These two powders are the SAME, made in the same factory, and the different recommended loads can only be explained by the techs using different production lots of powder. And if your manual lists loads for your favorite powder for 140 and 160 grain bullets, but not 150 gr, there's a good bet that another manual will have your load, or you can just extrapolate between the loads for the 140 and 160 grs. And again, your chronograph will usually tell you when you're getting warm by the velocity you're getting from your load.
And regarding the haphazard listing of the various powders, perhaps that is due to the sequence in which the powders were tested. There's certainly no other rhyme or reason.
"For every complex problem there is an answer that is clear, simple.....and wrong." H. L. Mencken