"I am not sure what exactly triggers ex-clearing..probably something a broker would want to hide their counterparty risks as well as their own. it is a very manual process"
The trades that you have seen since the DTCC freeze are ex-clearing. The manual process is why volume has dropped precipitously. Few brokers want to waste their time with it. More importantly as you can clearly see the trades and associated volume appear. The theory has been put forth that the alleged 50 BB in NSS was from non-reported ex-clearing. Who bought that many shares from a non-reporting broker? Short answer - no one. If those trades are not reported and do not show on price and volume then it is impossible to short a stock price down that way - which is the alleged motive behind NSS.
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