It seems like they know the responsible carriers, but not the originating customer of those carriers, probably because they're fly by night organizations. These

It seems like they know the responsible carriers, but not the originating customer of those carriers, probably because they're fly by night organizations. These recent orders are basically the FCC saying to the responsible carriers: "We've told you about this before, you've failed to uphold your promises to stop it, so here's a cease and desist and failure to comply and provide information about how you're complying will result in you being de-peered completely." And then telling all the other US carriers that they are now authorized to identify and block such calls from the responsible carriers without running afoul of the FCC rules that normally require all carriers to carry for other carriers. If the originating carriers get de-peered, the FCC will effectively allow other carriers to not carry any of their traffic, legitimate or otherwise and put them out of business.