One thing I do know is market makers have to repor

One thing I do know is market makers have to report their short sales to FINRA which show up on the daily short reports. However they do not have to report their short positions on the twice monthly short reports like brokers do. And by SEC rules market makers are the only ones allowed to naked short sell a stock. But they often abuse this loophole to trade for their own profits especially in OTC stocks.