Board Thread:Wiki Discussion/@comment-12633677-20131230012638/@comment-2020924-20140111223921

the problem as i see it is that they can be treated as both originals (as they are written by the author), yet it is not the original/first version (I usually mark it as "self-cover" under a song page's Succeeding versions, from the NND tag 「セルフカバ」)

And that's a really good question regarding derivatives o.o