It comes to a surprise to me that SharePoint OTB does not permanently save this piece of information.
- although workflow history and approval tasks holds this information, workflow history gets auto deleted OTB after 60days.
- creating an approved by column causes an issue with the approval workflow because the act of changing the metadata triggers a new approval workflow.
- SharePoint auditing logs are not designed to be read easily nor have ability to link back to lists for easy viewing
Create new list holding approved by, approved date, and document id (or some other identifier). Using this list, we can use SharePoint views to join the approval information.
Go back through the SharePoint audit logs and prepopulate this list.