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Stacy Chan from the Google News team said in the Google News Help forum that sometimes, Google may ignore the timestamp in the Google News Sitemap XML file from some publishers.
Why? Well, we've documented cases of publishers as large USA Today and BBC tricking Google News into thinking a story is new by updating their timestamps on their articles, even a day or so later.
Stacy said, "but also keep in mind that we don't necessarily use the sitemap's timestamp to avoid abuse." "We've seen instances where publishers will change the timestamp in their sitemap to try to "game" the system," she added. Finally, Stacy explained "this timestamp is considered in conjunction with the time our crawlers first discovered the article."
So you can spam both and maybe get away with it? :)
Don't do it, I hate seeing old stories pop up in Google News as new stories.
Forum discussion at Google News Help.
