It seems relatively straight forward (famous last words) to assess whether actual copyrighted text is embedded within the network. If you can prompt output that includes verbatim extracts when the copyright avoidance post-processing is disabled then you know that it has been consumed.
Of course whether that was purposeful or inadvertently as a part of the larger training set would not be determined but you would know that the text is in there.
Of course whether that was purposeful or inadvertently as a part of the larger training set would not be determined but you would know that the text is in there.