It seems to me that you've got 2 issues here 1.merge all the appropriate files into a single workbook and 2. produce a report that summarises what you are looking for.
For 1. You can try this add-in (see link) or search the forum on merging sheets.
RDBMerge, Excel Merge Add-in for Excel for Windows
For 2. PErsonally, I would suggest trying a Pivot table and seeing what that gets you.
Excel Pivot Tables Tutorial : What is a Pivot Table and How to Make one | Chandoo.org - Learn Microsoft Excel Online
You can summarize by Account Expiry time and filter for everyone with more than one position on the list or play with other formats to see if you can find one that suits your needs.