Thread:Derpy Diamond/@comment-25390652-20161111080158/@comment-25390652-20161111200856

Well, if it's already uploaded to the wiki, and you upload it again with the other name, we'll have 2 identical files → it's duplicate.

If you upload it again with the same name, that would replace the old file, which is fine, because the number of files will stay the same — 1 file.