Massive Increase in 404 Errors in GWT

[Marketing.SCG]

Last June, we transitioned our site to the Magento platform. When we did so, we naturally got an increase in 404 errors for URLs that were not redirected (for a variety of reasons: we hadn't carried the product for years, Google no longer got the same string when it did a "search" on the site, etc.). We knew these would be there and were completely fine with them.

We also got many 404s due to the way Magento had implemented their site map (putting in products that were not visible to customers, including all the different file paths to get to a product even though we use a flat structure, etc.). These were frustrating but we did custom work on the site map and let Google resolve those many, many 440s on its own.

Sure enough, a few months went by and GWT started to clear out the 404s. All the poor, nonexistent links from the site map and missing links from the old site - they started disappearing from the crawl notices and we slowly went from some 20k 404s to 4k 404s. Still a lot, but we were getting there.

Then, in the last 2 weeks, all of those links started showing up again in GWT and reporting as 404s. Now we have 38k 404s (way more than ever reported). I confirmed that these bad links are not showing up in our site map or anything and I'm really not sure how Google found these again.

I know, in general, these 404s don't hurt our site. But it just seems so odd. Is there any chance Google bots just randomly crawled a big ol' list of outdated links it hadn't tried for awhile? And does anyone have any advice for clearing them out?

[ThompsonPaul]

I'm just cynical enough to suspect this may be a byproduct of Google Webmaster Tools recent inbound link meltdown. Huge numbers of GWT users are reporting that their inbound link reports have basically lost most of their links.

What if, in dealing with the problem, Google has gone back to an older version of the links database, which might recover more of the recent links, but also pull back a whack of  those links it already discounted?

This is pure speculation on my part, but there's been so much volatility on Google's link reporting recently that I can't say I trust the data as far as I can toss it at the moment.

Have you tired a similar comparison to the data shown in Bing Webmaster Tools?

I'm sure I read of others encountering what you're talking about recently. Will see if I can find the references in case they found anything.

Paul