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If your back links have disapeared i would say that they have been removed, i dont think google removes links, just discounts tham, but i could be wrong

Mmm... it is not the webmaster that does the 301... it is your server that does it. I mean: the inbound link send to your old url page search engines bot (and users) follow that link and arrive to your site your server sees that a visit is directed to the old url the server then apply the rule you gave him via .htaccess (for instance) and redirect the visit to the new url of the page In this "transfer" a little bit of pagerank seems getting lost, that is why is alway better to ask to the owner of the site where the backlink is to update the link itself, if possible.