I noticed a few posts above describing flushes. As we approach the end of RC5, DNet will be re-issuing un-returned blocks at an increasing rate. Their latest graph actually supports using a 4-day turnaround, meaning that if someone downloads a block but doesn't return it in four days, there is a 75% chance it won't be returned, therefore it will need to be re-issued.
So, my advice is - don't let your cache of RC5 blocks get more than 4 or 5 days old, or you might not get credit for them. As we get closer to the end (95% complete), the re-issue rate will be more like 2 days.
Hopefully, TA will find the key before then, especially before HZ gets much closer.