I don't have thousands of dupes, my library isn't that big. I have a lot of books/fic/etc which I failed to organize properly in the beginning. Never thinking it will be necessary (never though I'll go from paperbacks to ebooks/electronic versions). All the files are scattered around and many are saved multiple times since I didn't find it when I needed it (now I use Everything search program which is amazing). I am still adding them since many have silly names (now I always save in correct names). Just recently found another folder with books and added it, most of them appeared to be dupes (probably an old back up) so I had to remove most of them from calibre. Basically, all the trouble is because of past mistakes - lack of organizing.
Clicking every second (mostly) entry gets tiring quickly. I just always looks for ways to automatize things
And because of my paranoia I never delete dupes - I just send them to another library. So if I accidentally choose the wrong entry I can always go and get it from the dupes library. That's why automatic selection doesn't scare me
I don't get how all plug ins work, how they are made etc. So I don't know when something is simple to do and something is basically impossible. So thanks for explaining.
I have way bigger problem with comics... Need to mentally prepare to go and straighten that mess out. And figure out how too.