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https://www.deepcrawl.com/knowledge/best-practice/site-redevelopment-using-deepcrawl-to-maintain-and-grow-your-audience/ https://www.deepcrawl.com/knowledge/best-practice/managing-url-redirects-301-302-307-and-meta-refreshes/ http://www.screamingfrog.co.uk/audit-redirects/

Might have to do with canonical urls.. pretty sure SEOMoz report doesn't take that into account when they tell you which pages are duplicate. Best thing to do is check out what pages are getting picked up by both sources and compare/contrast similarities/differences.