Few epubs have toc
That's a subjective conclusion. I keep noticing a message saying something like "This book does not have a table of contents."
Now since some at least of the books for which this comes up have a page listing all the chapters, I assume that a toc in the sense of the error message is something other than a list of chapters, maybe a way to jump quickly to a given chapter, like the clickable page numbers in some pdfs.
So what's the received wisdom? Should one put in a toc in an epub?
Now I'll post this and probably find that six other people have asked the same question, although I couldn't find it with the search function. <sigh>