cover:false does NOT return books without cover

[paulcolley]

I had this problem on a handful of books and fixed it by Library -> Library maintenance -> Restore database

Presumably at some point Calibre's database had gotten out of sync with the data on disk (as theducks pointed out, probably when I messed around with files without using Calibre)

Originally Posted by MarcDS

I have many books without cover, many epub and pdf, but also some mobi. When searching for cover:false I get an empty list.

I use Calibre 3.12.

What can I do to get a list of the books without cover?