Nice find. Here's the critical part (bolding added):
MMs routinely short during the day, but usually cover pretty quickly, often the same day. MMS have 3 days to locate, borrow, and deliver shorted shares before they are officially "short", much as you don't officially "own" your shares until the transaction settles after three days. Those daily FINRA numbers that show 20, 30, or 50+% of the volume shorted have little relationship with how many shares have been purposefully "shorted".