I have a question about the PKP PN. I see that “This is a free preservation option for journals using OJS 3.1.2 and newer, which are not part of any other digital preservation service (such as CLOCKSS or Portico).”
What about for journals whose content is archived in a national library’s longterm archive? Can/should they also use PKP PN, as an additional preservation service considering that “Good practice recommends that content is preserved in three separate services to be considered safe”?
I don’t see why not? It couldn’t hurt to have your journal archived in multiple places. There’s nothing that would explicitly prevent you from using the PKP PN if you were using additional service, it’s just that some are not in a position to have additional services available to them. As you point out, it is considered good preservation practice to be preserved in multiple places.