I just realised that according to UESP and a few other sources there is apparently a quest Neloth is supposed to give to retrieve a black book in Raven Rock Mine. Yet I have never come across it in any of my characters. Neloth in all my characters (just checked) has never offered Raven Rock mine as a 3rd location. Are these sources wrong?? Its funny I stumbled onto this, was looking up something completely unrelated at the time and this caught my attention .

Huh. I didn't actually know Neloth sent you looking for books outside the main quest line. The one you find during the mine business doesn't IIRC have anything to do with the Dragonborn MQ.... I thought it was just kind of a "teaser" lead-in to how Apocrypha works later on.

I always do Raven Rock Mine first thing when getting to Solstheim, so maybe that's why it didn't turn up for me as a quest from him? I did the whole quest line once back last fall, and now I just copy the books using Jaxonz Positioner to take home for my displays. I really dislike Apocrypha.... so I don't "read" them any more!

After you finish The Gardener of Men If you talk to him he sends you on 2 quests, to locate missing black books. One in White Ridge Barrow, the 2nd in Benkongerike and according to a few websites Raven Rock Mine. If you look in his dialogue it will say "Have you located any more Black Books" if the quests are available. He rewards 1000 gold to make copies of each one. But if you have already located a book he won't send you on a mission for it.

Yeah, that's why I thought he might not have said anything about the Raven Rock one, if you'd already found it. I don't think I talked to him after getting done with The Gardener of Men, I just wanted to be done with the quest line by that time! Well, hmm. I must have though, since I knew about the other black book quests for him. I didn't do them for him though.