currently if you have a very old listing up and it gets trades, once it is depleted because the original listing is beyond the prune date it will automatically delete itself, which also removes it from NOTS.
please prune based on most recent activity, so we can see who bought from the trade, where the random chunk of money came from, and which market has activity that i should pay attention to because my months old ask got hit.
i only caught this by accident. complete accident. one small trade hit, i had it open, closed it for a second, watched the listing vanish from the cx, tried to pull it up again and there was nothing.