Is it allowed to upload multitracks for archival purposes created by third parties (other than you) if they were released under Creative Commons?

I ask because culture always builds on the past and some older Creative Commons releases that were never on ccMixter or archive.org have started to become unavailable for one reason or another.

For example, David Byrne and Brian Eno’s My Life in the Bush of Ghosts Remix Site which launched in May, 2006 no longer works. You can’t download the stems there anymore just because their old site is broken. https://creativecommons.org/press-releases/entry/5896

Another example: Jonathan Coulton released the stems to a large number of his biggest hits under a Creative Commons license, making them totally legal to share (at least in multitrack form) but he only actually distributed this release on a USB stick that was given away to a few people at concerts. (it explained the Creative Commons license in a readme file I believe) This material is legal to share — the only question is whether it’s allowed to be shared on ccMixter or not.

ccMixter is a creative community and not really set up as an archive. However, I imagine archive.org may be a good place to check out.