...

Until "Mark as Complete" button is clicked in E-Verify, Section 3 fields are editable for the I-9 Specialists. After marking E-Verify activity as completeOnce this activity is completed, you are not allowed to edit Section 3.

Let's access completed Section 3 activity before 'Mark as Complete' button is clicked in E-Verify. Notice, edit button is enabled in Section 3. Click Edit. 

...

After 'Mark as Complete' is clicked in E-Verify, the edit button is disabled in Section 3. Below example shows no Edit button activity will be marked as complete.

Click Complete I-9 link in the left nav and access Section 3. The 'Edit' button will not appear in Section 3.

How to record new/changed work authorization documents?

...