They are not on the manga, themselves, but on the books that condense all of the different dates from Shonen Jump, for instance, into books that are only for that story.
For instance, Dragon Ball, Bleech or Prince of Tennis. It takes like 3-6 months of regular manga sections to but together enough to make one of the books.

Rothbardian_fanatic

I didn’t know that about the manga spines! I will check out your observation the next time I patronise a bookstore

cryotosensei

BooksAndArticles

A Japanese bookstore

I always used to spend a lot of time in the manga section. I got the full set of Dragon Ball and Dragon Ball Z concentrated books. They have a neat design on the spine of the books that shows part of the story across all of the books’ spines. I still have them here and they have amazed some of my younger visitors from Japan.