I have a client who went through a re-brand earlier this year, and have been using the redirection plugin to provide the 301's for the old site to the new site. In working with the Google Webmaster tools, I've found that many of the 404 errors it's presently finding already have a redirect set-up for them. Perfect example is that the report this morning showed 51 total 404 errors, but only one of them didn't have a 301 set-up.
After performing a full analysis of the redirection tables in the database, I found that 32% of the URLs I've attempted to redirect aren't working. I have duplicate entries in the database (roughly 380 out of 1580 redirected URLs), and the duplicate redirects aren't working at all even though they are valid.
Any thoughts on this? If the number was lower, I wouldn't have an issue with it and tell the client it's an issue with Google over the plugin.
This isn't at all urgent, though I'd like to see if there is a fix for this so I don't have to keep charging the client for more effort than is necessary.
Thanks in advance.