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So how does Google react
It starts throwing things into the index, then throwing them out again. In, out, in, out, shake it all about. :)
I stuffed something up the other day, which led to a whole load of 'extra' URLs leading to the same pages. I swear they were only visible for minutes, but Google (darn it) found them and now I'm watching the supps index change by the hour while I frantically try and 301 the 'extras' to a single, correct URL.
Moral of the story: If there's a possibility of an incorrect URL causing 'duplicate' issues, Google WILL find it. MSN and Yahoo seem to stick fairly rigidly to the sitemap, while Google goes walkabout. 301 asap.
Many of the old URLs will remain in the index for many months, maybe even a year. Your redirect will get the visitor to the correct content anyway.
Once any of the old URLs are shown as Supplemental Results you cannot control what Google will show for those. Ignore them and move on. Google will do what it has to do from then on.
When redirecting "index.html" to "/", would you wait until after Google has seen (or cached) the changed links in your nav, or would you apply the redirect as soon as the nav change is made?
My instinct had been to apply the redirect immediately, but I've discussed this with those who feel that, in this case, Google should see the changed link before the redirect.
Their thinking is that you don't want Google believing you're linking to one url of a page while you're redirecting to another. As Google already sees more than one url for the page, I assume the redirect timing isn't going to change the dupe issue, and that it's more a question of consistency in Google's eyes, if that's something Google weighs.
[edited by: Robert_Charlton at 2:31 am (utc) on May 3, 2007]