A note on the file renaming behaviour: If you copy and paste (i.e. duplicate) a file, then "(copy)" is added to the end of the base of the file name, but if a name collision occurs while adding files externally, then jAlbum adds a space and an increasing number to the new file in order to resolve the name collision, this as it's not certain to be a copy.
Excellent distinction to make. In my case, too, the duplicate file names are, indeed, not copies of the same image.
Why do we end up with duplicate file names? Simple. For the family album, I rename files to keep track of dates. Why not rely on the camera date? Because when I harvest images from someplace like Facebook, the metadata are gone (I hate Facebook with a passion). So, if I grab an image today, I'll rename it s2020-01-17.jpg ("s" for "still image," as opposed to "video"). If I'm grabbing several images, I might start adding "a", "b", and "c". But during busy vacation and holiday times, when there are images coming from siblings, nephews and their wives, and the occasional in-law, it's very easy to end up with duplicates. When the little ones get old enough to start taking photos, it's going to get worse.