This is a tough one for me, in part because it depends on what you consider a "concept album". You have full on narrative-driven albums, and then there's albums with a central "concept" or theme as its focus.
It's not really a thing, but I do make that distinction, a "themed" album.
I consider a concept album something that tells a story, like SFAM or Mindcrime.
I consider a themed album something where the songs have a unifying theme, but they don't tell a story from beginning to end.
if DT had released the title track of Six Degrees as a standalone "album", I would consider it a themed album. There's no story told there, it's just that all the "songs" are about the same subjects, mental diseases / issues.