Alleged copies. A reply noting the allegation and pointing toward the evidence is the best solution. If any copyright holders care to notify PerlMonks (probably via The Perl Foundation, though "/msg gods ..." might give a faster response) of their own claims of unauthorized copying (and request of specific desired action to address the alleged violation), then action will be taken to respond to such claims.
IMO, PerlMonks administrators should not be in the business of judging evidence trying to determine the legal status of contributions, nor of trying to second-guess the desires of alleged copyright holders.
If you are concerned about some copyright holders, then feel free to contact them, notify them of your suspicions of unauthorized copying, and invite them to contact the site admins if they wish action taken regarding the (allegedly) copied material.
I see more value in preserving the accurate record of the (alleged) infringement and even of links to (alleged) copyright violations (such as on-line copies of Perl books) for the possible benefit of copyright holders hoping to investigate any violations over trying to second-guess alleged wishes of alleged owners.
The documentation of the allegations has more moral value in my book then trying to pretend that it didn't happen or that the linked-to material does not exist.
And I believe that site admins attempting to determine legal status and take action based on their guesses actually opens up the site to more potential for legal troubles than does a laissez faire policy.
In reply to Re^2: How should Perlmonks deal with Plagiarism? (legalese)