Enabling Certificate Snapshots
Once a learner's certificate has been generated, it is saved in the database and “locked” so that changes to the templates will not change the generated certificate. This ensures that the learners will always have the original certificate saved even if the template is inadvertently changed. If you need to change learners’ certificates after they have been generated, you may clear the certificate snapshots.
Click "Settings" link.
Check the "Use certificate snapshots?" checkbox.
Click "Save configuration."
Certificate snapshots are typically enabled by default at site setup.