Having moved a site across to Magento, obviously re-directs were a large part of that, ensuring all the old products and categories linked up correctly with the new site structure.
However, we came up against an issue where we needed to add, delete, then re-add products. This, coupled with a misunderstanding of the csv upload processing, meant that although the old urls redirected, some of the new Magento urls changed and then didn't redirect:
For Example:
mysite/product
would get deleted re-added and become:
mysite/product-1324
We now know what we did wrong to ensure it doesn't continue to happen if we weret o delete and re-add a product, but Google contains all these old URLs in its index which has caused people to search for products on Google, click through, then land on the 404 page - far from ideal.
We kind of assumed, with continual updating of sitemaps and time, that Google would realise and update the URL accordingly. But this hasn't happened - we are still getting plenty of 404 errors on certain product searches (These aren't appearing in SEOmoz, there are no links to the old URL on the site, only Google, as the index contains the old URL).
Aside from going through and finding the products affected (no easy task), and setting up redirects for each one, is there any way we can tell Google 'These URLs are no longer a thing, forget them and move on, let's make a fresh start and Happy New Year'?