78, the loading manuals can't cover it all. Typically, they assume that you are after top velocity and offer a starting load a reasonable amount under the top load. It's not just Lee.
The best book for your purposes would probably be Ken Water's "Pet Loads". That's more of a collection of articles on loading for specific cartridges than a straight loading manual although it has thousands of loads listed. It has much more information than any standard manual.
Other than that, you can ask here. The members here have hundreds of years of collective loading experience. You'll get all sorts of horror stories about load data off the net, but when you get similar answers from several posters and a day goes by without anyone screaming of danger, you're pretty safe. Just check the data against the manual you have and ask again if anything seems questionable.