But they could be blocking it with robots.txt or some other excuse. It seems like an incredibly rare exception, what news site would block being crawled and indexed? They also are archiving domain info I'm sure. If they wanted to stop this, they have the data.
So it's my content, on a domain I no longer own or control.
How could I prove to Google that the content is mine?
You take over expiring legitimate domains, and ideally immediately (before Google notices) put up almost the same content, but with a link to whatever site you're actually interested in giving better search ranking to.
Repeat this 1000x and you can apparently make enough headway that people put time and money into the approach.
How do you know it's backdated if by the time you crawl the articles have appeared on both sides. How do you know which was published first? This attack can be performed faster than the re-crawling frequency.
One is that it's a business decision, where they know these cases may exist but they took the decision that it's not worth the extra overhead. Second possibility is that it's an oversight, essentially a "bug" in the system.
Either way, it appears that Google had not yet identified this as a serious problem.
I give credit to them for having a Transparency Report so that others can pick up fraud and abuse which they themselves may not have already found to have been a problem; an essential safeguard. I also view projects such as Lumen as being of increasing importance.
Google crawls surprisingly little of the web, even on web sites it knows about. That’s why web developers have to use site indices and Google Webmaster Tools to tell G that stuff exists on their sites, hoping that it will be discovered and indexed.