@Kay Thank you Kay! This is a great start. Have seen a great deal on blockchains but will definitely check these out as potential sources.

Also been reading up on "dark data" (not the greatest name) and am becoming worryingly aware of for example taking multiple photos of the same subject and just letting those photos rest on my device, copied onto cloud servers, to be hosted by electrically powered data centers for all foreseeable future never to be used again.

Multiplied by a few billion devices…