Yes the changes in data are confusing. I look at 4 or 5 different manuals , of fairly recent publication and check the powder manufactures site for data. I then average all the max and min loads to get an idea of a logical min and max charge.
Some data is rather high and some is rather low...by averaging them all I usually come up with a good place to start and have a good idea of what maximum is. I never start with a max load, start low and work up. Maximum loads can get you in trouble so approach them with caution.
My go to first books are Lyman Cast Bullet Handbook 3rd Edition, 4th Edition, the Lyman Reloaders Handbook 49th Edition ( I will get the 50th soon) the newer Speer and Hornady manuals.
Then check the powder mfg. data .
Good luck,
Gary