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Is Google webmaster Tools data completely inaccurate, or am I just missing something? I noticed a recent surge in 404 errors detected 3 days ago (3/6/11) from pages that have not existed since November 2011. They are links to tag and author archives from pages initially indexed in August 2011. We switched to a new site in December 2011 and created 301 redirects from categories that no longer exist, to new categories. I am a little perplexed since the Google sitemap test shows no 404 errors, neither does SEO MOZ Crawl test, yet under GWT site diagnostics, these errors, all 125 of them, just showed up. Any thought/insights? We've worked hard to ensure a smooth site migration and now we are concerned. -Jason