The ODATA REST API on SharePoint online doesn't provide for querying for a specific version of a list item. I have an app that can only interact with this API.
Accordingly, for a list in which I need to be able to obtain values for past versions, it seems I need to roll my own 'history' by using a workflow triggered on update of items, which copies the record either to the same list, or another list, with a version number.
I can do this, but can't figure out how to obtain the 'before' values (the values prior to the change constituting the update) within the workflow where I'm setting column values.
How can I get these 'before' values in a workflow that is triggered in an update?