Three Sisters Series x 2

[willaful]

Both fixed.

Re the first issue: There's no easy way to fix this that I know of, so I deleted half the books and then started a new series.

The second problem was caused by adding the series to the book -- if the series already exists, you need to add the book to the series. That is, go to the series page and add it there. Adding a series on the book page creates a new series. What I did here was go to the new series page, edit, and click the delete button at the very bottom of the page. Then I went to the old series page and added the missing book.

[willaful]

Yes, the first one probably happened when they first started the series pages and did a mass auto series creation. There were lots of these and I guess there are still some lingering.

Don't feel bad about your mistake, we all make mistakes, and at least you noticed the problem and did something about it.