When submitting content to Google news and then making amendments to the article Google will not retrieve the new data from the new amended article. The reason for this is that Google have already retrieved the information of the original article and will not bring the new article into the index. Google are currently working on this issue and will hopefully have the technology to retrieve new adjusted content. To read more on this subject follow this link http://googlenewsblog.blogspot.com/2008/04/psstsecrets-of-google-news-exposed.html

When we realise that Google have the technology to detect duplicate content and tracks the original source of the content, keeping the orginal content in cache ignoring the duplicate content in its index, then publishing duplicate press releases is of no benefit to your website. So when wanting to benefit from gaining exposure and perhaps in the long run, backward links, then having the press release submitted to 50 press release sites is of no benefit. The only way multiple PR is beneficial will be when each press release has unique content before submission.