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> Very recent changes are not captured by backup systems, no matter how competent they are.

Depends, there's backup software for Windows that will watch for file changes and backup immediately. Usually enterprise targetted. You could certainly do that on other OSes, possibly with less nice apis; a half measure would be taking filesystem snapshots continuously or once a minute or ???.

There's filesystems you can use on cd-r/dvd-r, although that doesn't sound pleasant, that would give you the option to go back to any version.