Krieghoff made some changes to enhance the durability of the the hammers, springs and firing pins etc. over the years. Its not at all critical to do a upgrade, nothing is wrong with any year, but if you want it to be the same as the newest year, its called a upgrade.
Almost all K-80 parts except springs, have a lifetime replacement warranty, if something breaks it will be replaced with the newest part in most cases. I know guys tha have very early K-80's that they shoot constantly and have ever done anything but a occasional annual. They all work the same regardless of what year parts are in them.