Thr first subject you want to research is "bitrot", which describes all the various ways that data at rest (just sitting on media) can be corrupted and lost.

Flash storage works by trapping electron charge inside microscopic transistors. If enough charge is lost over time, bits can begin flipping, and if enough bits are flipped, data can become corrupted or lost. This means a flash drive just *sitting in a drawer* can slowly corrupt the data written to it. For this reason, I also do not consider OpenDimes to be cold storage.

Archival storage would be someything more stable at rest, like tape drives or (my favorite) Blu-Ray media that adheres to M-Disc standards.