Originally Posted by kovidgoyal
The problem is that there isn't a reliable enough mechanism on the PRS500 to achieve true syncing. This is primarily because the 500 has no internal clock and times drift. So there's no reliable way of knowing when something is newer.
I guess that one way to do it would be to record the timestamp on the external file system in your database, and recopy the file to the Reader if it had changed to a later time.