I found the problem with the duplicate books and it wasn't a Nook problem after all. I copied those files from my Dropbox folder to the Nook and it seems Dropbox duplicated them. I had updated a few books on my laptop and when they no longer matched the files in the Dropbox folder on my little HP Stream (named Tweety since all my computers are cartoon characters) it created a duplicate in my Dropbox folder, appdending "Duplicate from Tweety that's been modified". Personally that seems like a Dropbox bug but they might think it's a feature. Of course I'm right.
Anyway I'm glad to know the Nook wasn't the cause of the problem.
Barry