Save a checkpoint
Use File → Versions → Save Named Version (⇧⌘V). Give the version a name that explains the milestone: “Picture lock before captions” is easier to recognize than “Version 7.”
A named version records an intentional state. Autosaving keeps the current document up to date; it is not the same editorial decision.
Compare and restore
Open Versions & Review to inspect available checkpoints and compare edits. Check the relevant sequence and resources before restoring. For a major experiment, duplicating the sequence can also keep two active alternatives close at hand.
After restoration, review picture, sound, titles, and caption behavior in the actual sequence. A difference list directs your attention; playback confirms the result you want.
Retain source media
Versions do not make missing media reappear. Keep referenced originals available and use a collected project for a portable handoff. Before replacing a current cut, save a separate checkpoint or copy if you may need to return to it.