The Transaction Matching file in AR contains a list of invoices and the dates they were paid (or credited or adjusted or applied by any document type). This should be an interesting file to look at, as Steve alluded to in a previous posting.

You might also want to watch the GridView 9.0C webinar, as one of the workspaces demonstrated was linking the AR transactions and matching file together in a very similar way to what you want - it's around the 28 minute mark of the video.