Many experienced with search engine optimization know that Google’s backlink feature, the link: command, has long not returned all the links Google actually knows about for
a particular page. Nevertheless, the issue continues to come up again and again, as new people stumble onto the problem.
Google recently expanded the number of links it shows, but it still doesn’t show all of them. That’s not going to change, but at least Google may finally update its web
site to change the current wording about the feature, to make it clear not all links are shown.
More about the issue, with a long post by GoogleGuy, can be found in our forum thread Google Say Not
Reporting All Backlinks.