There is not currently a direct data linkage between a filled hold in old_reserves and the checkout that filled it in (old_)issues. It'd be helpful if we could put the issue_id into the old_reserves table to make that explicit.
On a similar note, it would be helpful to add issue_id and reserves_id to the statistics table. (I've found the timestamps across statistics, issues, reserves and action_logs don't match up neatly.)