Nice find. Here's the critical part (bolding added):
By signing up for our RegSHO Compliance Service, your trading is monitored daily and they identify short selling, illegal short selling, manipulative market maker activity and alert the media when a short squeeze begins and when forced buy-ins occur because they were able to get broker dealers, FINRA or the SEC to force “buy to covers” upon short sellers that have not located, borrowed and delivered shares shorted by T+3.
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".