Auditing workflow task approval

I know there are a number of threads about how the workflow task history is not good for auditing purposes. There is the audit feature in SharePoint (I'm using 2013 SharePoint online) which I've turned on. That will log whenever a content item is changed. It will also log whenever a workflow task is changed. So that's good, I can see who approved the tasks. But similar to the problem everyone is trying to solve, there's no association that I can see logged showing which tasks are associated with which workflow. My users want to find out who approved an item. I can go from the item and find the workflow instance ID, but there's nothing in the logs that I can find that corresponds to that. I haven't had one of the workflow instances get deleted since I turned auditing on, but maybe that gets logged and will show the necessary information?

Basically, given an item and its workflow GUID, how can I associate the workflow tasks in the audit report? Must I download the information every X days and look through that?