Things like this happen more frequently than one would think.
This happened to me with a certain torrent that was replaced by a new one after a while.
I had downloaded most of the files of the old torrent, and then downloaded a new one.
In the new torrent all the old files were the same, but extra files were added.
So I copied the files to the location of the new torrent, deleted the old torrent, and performed a hash check. I had then the new torrent almost fully downloaded, and started uploading the data I already had, while downloading the new.
I can't recall much of the info, but I do remember that I had much more upload and download than I should in the column.