Like I stated there could very well be some DTCC "service" that is restricted apart from the CNS system or T4T that the public will have no direct knowledge of, but the brokers will. And that may be what is effecting the broker's position or the broker's restricting the stock.
But even before all this new attention with the DTCC, broker's for years have made their own call on particular stocks and have restricted trading in their "house" (even though the DTCC CNS system was available) while other brokers would trade the stock. Brokers now overall are just getting more critical and the DTCC and SEC are cracking down this year more also.
Market Data 
Markets 
AI
