Training doesn't last forever. Martyn's Law expects staff to be refreshed regularly, and PROVA handles that automatically.
How often
Each site has a training frequency set from its assessment, typically annual, sometimes more often for higher-rated sites. Your Premises Controller can see it on the site's Staff page.
What happens at a reset
When the period ends, everyone's progress for that site returns to zero and the videos need watching again. Staff receive an email telling them their refresher is due, and the Premises Controller is notified.
If your progress disappeared
That's a reset, not a fault. Your previous completion is kept in the site's records; the fresh run is what's needed now.
Changes to a plan
If a plan is republished with significant changes, the related video may need re-acknowledging before the next reset, so staff are working from the current procedure.
Chasing stragglers
The Premises Controller sees who's completed and who hasn't. Reminders go out automatically to anyone who hasn't finished before the due date.