My take on the rule of four is that DVC has to have time to recover the cost of that non-DVC trip and four months or less just ain't gonna cut it. They don't give us access to those trips out of the goodness of their hearts. They have to resell the lodging your points represent before those points expire (four months or less).
So even if you have a Sept UY (points expire on Aug 31) and you call on Aug 29 for Aug 30 and 31 (and DVC lodging is available), you can book a stay at a DVC resort for points for those days.