SharePoint 2013 workflow vanishes after approval when manager name changes

I have an issue in SharePoint 2013 online where previous workflow approvals no longer show as having been done when a user's (she got married) last name changed. We sync with Active directory nightly. All workflows done after name change appear but nothing prior to name change. Any ideas on how to get those to show? Unfortunately these workflows are an audit trail on documents for our accounting group - so i have to display somehow!!! All help is appreciated.

Thanks,
Diana