Understanding the gaps prevents unpleasant discoveries.
NOT COVERED BY ANY BACKUP
Data written after the backup was taken. Orders, form submissions, comments and content created since are gone if you roll back.
Anything stored outside the hosting account: a payment gateway's records, a third-party CRM, an external mail service.
Domain registrations. A backup does not restore an expired domain. Third-party licences and API keys, unless they happen to be inside a config file that was backed up.
FREQUENTLY MISSED
Email, if you use a backup plugin that only covers the website. Plugin backups almost never include mailboxes. Files stored outside public_html that a partial backup did not include. Cron jobs, if you restore only files and databases. DNS records held at an external provider such as Cloudflare.
THE PRACTICAL RESPONSE
Keep a full account backup periodically, not only application-level backups. Export important data from third-party services on their own schedule. Note down cron jobs and DNS records somewhere outside the server. Before a rollback, export anything created since the backup so you can re-import it afterwards.
