They don't change very fast, but they do change
Newer manuals will have newer cartridges. If you get a manual older than about 2005, you will find no loads for Trail Boss powder because it hadn't hit the market yet. Likewise the 460 and 500 Smith & Wesson cartridges.
Of course, there are uses for older manuals, too. If I have a 1990 can of powder, I would use a 1990 manual, just in case the formulation changed a bit. Of course, I would also cross-check with a current manual and visit the powder makers web site in case some issues became known (Like Blue Dot and 125 grain bullets in .357 Magnum and in 41 Magnum for all bullet weights for which Alliant issued a warning letter in July 25, 2008) in the meantime.
Recipes have changed over time, apparently mostly going down. I don't know if publishers have become more cautious or if measuring devices have become better (I have heard both explanations).
Procedures have not changed very much at all, but some examples might mention equipment that did not exist a decade or more ago.
Last edited by Lost Sheep; December 30, 2012 at 11:46 PM.