Right. All first letters were not certified. Then they sent 25 certified ones for Sept 6 (only 20 could make the cut). Like Garbage said, more than 5 people declined so they sent out a handful more certified letters to fill Sept 6.
What surprises me a bit is that someone in the "mid-30s" got an offer to the September 6th class. That could be roughly 35 letters sent out for a class of 20 and that's a pretty large amount of bypasses.