I won't get too in depth on the subject but heres a couple ways so you understand I know what I'm talking about
The way FTD's (fails to deliver)show up is when they happen through DTCC.. but market makers can go outside of DTCC and clear these shares without it showing up... this is known as ex-clearing.. So pretty much it is like doing a black market sale... the market maker is given money for something that is fake, and because the DTCC doesn't know about it, it doesn't show up on the REG-sho list..
Ok, heres another and then thats it...
Continuous Net Settlement is when a BD has a net surplus of shares with DTC, DTC loans to the short BD which hides millions/billions of counterfeit shares that never make it to Reg SHO list. It would take a subpoena to get disclosure.
The point is there are plenty of sneaky, underhanded things that go on in the markets. Why? Because when theres a lot of money at stake, corruption is always present
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