Thanks, Jeff, for the life-cycle chart.
A couple of ideas come to mind: - When unpacking objects from a pack, it should be fine to set their date to that of the pack. After all, they're at least that old. - We could put unreferenced objects into packs whose date is the most recent of any of the contained objects. - We could then group unreferenced objects into packs based on age, so their ages sould not be affected too much by the preceding operations.
That still produces a noticeable number of packs, which isn't good, but maybe it's better that keeping thousands of loose objects for a month...