The safest thing to do is check at least 3 official sources, start at the lowest starting load and work up to the lowest max. In the real world, most folks work toward the highest max.
Load manuals are for reference only. You might run into a starting load that is actually max in your gun with your components. This should be rare but it does happen. You might also find max loads that are below starting loads in another book, this is actually not all that rare.
The Lyman 49th, on page 57, shows that changing nothing but primers in a .308Win load can make a difference of 2,600psi. That's about 5%, all by itself. Considering that every component you use is different than theirs, it's quite understandable that different manuals have different suggestions.