the songbook WAS updated.
When I was young, the songbook had a Pepto-Bismol pink paperback cover. Then in the early to mid 80's, we got an update of the songbook with a brown hardback cover. Mostly new songs were added--took us forever to learn them. A lot of off-key humming for awhile. I also remember they changed the tune to the last song about paradise, but same words--I think they got sued for plaigerism. It really confused me when I was young, because the last song was always my favorite, and I would try and sing it the old way. The new tune never felt right.
Edited to add: "Keep Your Eyes on the Prize."