Yes, FTD data is somewhat unreliable. Due to the fact that reporting parties are self-regulated, SEC retains oversight but only polices in the event of reported misconduct. I treat all data as smoke. If you see it, it pays to look deeper for the fire. DBMM definitely had some smoke.
The means of regulation by the SEC is fines, but seldom more. Most MM's see upwards of 1 million a year in fines for failure to properly self-regulate. Citadel is one of the largest offenders.
I noticed the conflict of opinions in DBMM regarding naked shorting. I wasn't aware this was debatable. It occurs constantly. The depth of which and circumstances can be open for discussion, but the occurrence is not.
NSCC expanded its CCP services to include SFT's. SFTs are lending transactions typically used to cover short sales or fails to deliver. The fees can be lucrative and have to be renewed constantly as long as the FTD persists. Problem here if abused, this system can carry on for a long period in an otherwise illiquid stock.
Another form of behind the scenes manipulation that is rampant within the markets.
Market Data 
Markets 
AI
