I think I see the problem now. If it's looking at the 50 items that have gone the longest without being updated, but the allies get updated frequently, then they never make that top 50 list. Once I have updated all of the top 50 that have listings, I only get repeats of the 10 or so that have gone a long time without updates, but have no listings now, so I can't update them and get them out of the top 50 list.
What would be ideal is if it looked first at what I haven't updated for over 24 hours, and then grabbed the top 50 of those that have gone the longest without updates, but I assume that woud be a much uglier programming task since the top 50 list would have to be generated for each user instead of globally.