When I create a song I immediately upload it to dropbox. That way I can make sure I can recover it if my hard drive is failing (as i don't have redundancy) but also to show I have a tangible form of the song which is on dropbox as evidence.
There is also copyright registration services that will store the file, for example songrite, CCS (in the UK) etc.
My question is what happens if dropbox or CCS go bust? is my proof of having recorded it at a certain date gone? And how should I mitigate it, is taking a screenshot enough?