>>24553624 (OP)Longhand drafts that they sent to typists that wrote them up professionally. Alternatively some authors would revise and type it up themselves though this required considerable skill.
Of course that’s not the end as the books would have to be edited and finally typeset and errors would hopefully be ironed out in the process (including proofs of the typesetting) but sometimes new errors were introduced instead.
It’s worst for anyone writing for magazines or similar print as the editors could be ruthless both in trimming stories and outright changing them. This is why you get some scholarly insights from comparing versions along the way. Some early edits are actually in print for this purpose.
https://www.spbooks.com/150-1984-9791095457114.html