Google crawling Error?

I have a site and i am doing all the SEO process except paid links. but Google has not updated its cached date for few pages in my site. But its updating indexing Status. When Google update its indexing status it must crawl all webpages. Right? I am so confused about this. Plz explain in detail?

Ever since we released the crawl errors feature in Webmaster Tools, webmasters have asked for the sources of the URLs causing the errors. Well, we're listening! We know it was difficult for those of you who wanted to identify the cause of a particular "Not found" error, in order to prevent it in the future or even to request a correction, without knowing the source URL. Now, Crawl error sources makes the process of tracking down the causes of "Not found" errors a piece of cake. This helps you improve the user experience on your site and gives you a jump start for links week (check out our updated post on "Good times with inbound links" to get the scoop).

In our "Not Found" and "Errors for URLs in Sitemaps" reports, we've added the "Linked From" column. For every error in these reports, the "Linked From" column now lists the number of pages that link to a specific "Not found" URL

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