If the only permalink setting is %postname% what happens in the case of old duplicates?

I am tempted to change my blog to be site.com/postname.

I know that for new posts WordPress is smart enough to add a unique number to them, but what about old posts that would get updated?

I can run a database check for duplicates and manually fix them but I was wondering if this was already covered by some WordPress magic?

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Any time you have a duplicate slug for a post or taxonomy, WordPress just adds ‘-2’ to the end of the slug.

I don’t believe it’s covered by WP magic; and lately there’s been much discussion of how bad it can be performance-wise to use %postname% alone, for example http://digwp.com/2011/06/dont-use-postname/ You might have better luck with %year%/%postname. Best of luck!