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Google Can and will index pages, even after nofollow links are added. It might me that a different domain is linking to that page thus the nofollow is rendered useless. The yoast plugin adds a noindex.  The noindex is only applied after recrawling plus some day's. you can check this in google by looking "in cache" and see the date. Even so, google still can and sometimes will index it. (eg if you do noindex on you whole domain, google will still hold you homepage in google for a long time) Google makes a decision based on their parameters.