In my latest image with IC 1340, the dragon head, I noticed a very faint band. I haven't noticed this before, probably because I haven't been using such narrow band filters. But it was clearly there. When I checked my bias frame, nothing was showing in that location. But when I checked a long exposure dark frame, sure enough, the band was there.
I decided when processing some additional data I gathered last night to try processing with and without a dark and see what happened. Sure enough, the dark removed the band. I'll be using them again, at least for this narrow band work.
First the image processed without a dark. Notice the very slight band just to the left of the left portion of the nebulosity.