I am consulting someone for a problem related to copied content. Both sites in question are WordPress (self hosted) sites. The "good" site publishes a post. The "bad" site copies the post (without even removing all internal links to the "good" site) a few days after. On both websites it is obvious the publishing date of the posts, and it is clear that the "bad" site publishes the posts days later. The content thief doesn't even bother to fake the publishing date. The owner of the "good" site wants to have all the proofs needed before acting against the content thief. So I suggested him to also check in Google the dates the various pages were indexed using Search Tools -> Custom Range in order to have the indexing date displayed next to the search results. For all of the copied pages the indexing dates also prove the "bad" site published the content days after the "good" site, but there are 2 exceptions for the very 2 first posts copied. First post:
On the "good" website it was published on 30 January 2013
On the "bad" website it was published on 26 February 2013
In Google search both show up indexed on 30 January 2013! Second post:
On the "good" website it was published on 20 March 2013
On the "bad" website it was published on 10 May 2013
In Google search both show up indexed on 20 March 2013! Is it possible to be an error in the date shown in Google search results? I also asked for help on Google Webmaster forums but there the discussion shifted to "who copied the content" and "file a DMCA complain". So I want to be sure my question is better understood here.
It is not about who published the content first or how to take down the copied content, I am just asking if anybody else noticed this strange thing with Google indexing dates. How is it possible for Google search results to display an indexing date previous to the date the article copy was published and exactly the same date that the original article was published and indexed?

In this video from Google Webmasters about content, https://www.youtube.com/watch?v=y8s6Y4mx9Vw around 0:57 it is advised to "archive any content that is no longer relevant". My question is how do you exactly do that? By adding noindex to those pages, by removing all internal links to that page, by completely removing those from the website? How do you technically archive content? watch?v=y8s6Y4mx9Vw