Reasons for ranking drop

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Michael Martinez: If this is for the same Website I looked at before, I see it listed at no. 2 when I search for the company name. Your eBay store seems a little less cluttered to me than your Website. I`m not sure what you`re seeing. Are you logged out of Google? Did you clear your cookies?
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  Vinson Chan: in the past when i search jotrin ，the rank is no.1，now it drop ，it is no.6 ，but i see the information at search-console，the website page rank is 17
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  Vinson Chan: The index of the website has fallen more severely., it has dropped from 4 million to 300, 000 now. in the past 3 month
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  Michael Martinez: So the Search Console ranking data is an aggregate value, averaged over the reporting window (how many days you`re covering). The averages tend to change as you shorten the window. Google began excluding some query data on August 1. Does it look like your reports were affected by that change? The index coverage could indicate something else. Was yours one of the sites using "nofollow" attributes on some internal links? That would disrupt internal crawl and indexing and it could take weeks or months to recover from that. I just glanced at your site today and did not see any internal "nofollow" attributes.
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  Vinson Chan: Michael Martinez yes，last time you tell me my site should not have "nofollow" attributes，i do that。2.index coverage report that some product detail page excluding a lot
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  Michael Martinez: You have a lengthy "robots.txt" file. Are you sure you`re only disallowing directories you don`t want indexed? And did you sample the coverage report to verify that Google is telling you the truth about pages not being indexed? In the new Google Search Console, on the Coverage report, examine the list of excluded pages. Pick one URL and click on the magnifying glass icon. GSC loads another screen and examines the URL in its index. It will tell you if the page is indexed in Google or not. The Coverage report can be filled with a lot of false-positive exclusions (I have no idea of why - they just don`t seem to know what they are doing these days).
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  Vinson Chan: Michael Martinez yes , not mistake, just not index , have crawled