Versions are saved every couple of minutes while you type, when you leave a note, and before any big deletion. Restoring saves the current text first, so it can be undone. Kept for 30 days.
Deleted notes stay here for 30 days, then are removed for good.
The zip has each note as a .txt or .md file plus note-gripe-backup.json (notes, trash and history). Import takes that JSON or .txt/.md files, always as new notes, never overwriting. You can also drop files onto the page.
note-gripe-backup.json