I was advised to use just one manual until I had enough experience to deal with variables. For the first five years I used just that one, a Lyman #43, and never felt I needed anything else until several new cartridges and new powders came on the market. By that time the differences between manuals was no big issue to me. Today I have over two dozen, bought at an average rate of one every two years, but I still use that old Lyman more often than not.
As you may expect, I also suggest new guys stick to one manual until you get well grounded, otherwise you'll often be confused for no good reason.
Book OAL is what the book makers used to develop the listed data, it's no more a law for the rest of us to follow than their powder charges are.