It is a confusion.
Dave and Larry wrote a book together, Dave is the main author and Larry is the coauthor.
coauthor
no.
According to the sources I've found on a quick search, you should hyphenate 'coauthor', i.e., it would better be: "co-author".
The word coauthor is a noun. The plural noun is coauthors.
Generally co-author should be hyphenated, but the relaxed rules of modern times often present coauthor as one word
Examples of co are cooperate, coworker, coauthor and so on.
johnjay
Richard P. Bland
It means that they are sharing credit. There is more than one author.
It means that more than one author wrote a book/article together.
He didn't . Both Adams and Franklin helped Jefferson with it .