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This often happens if there is a redirect inbetween the sites and so the referrer gets lost which would account for that difference. It could also happen if you have a 404 or slow page so no GA visit is recorded but that would lead to less of a difference. I would suggest adding active tagging to the link and as above reply, ask for a free extension. By active tracking you just need to add the following 3 query parameters with meaningful values such as: ?utm_source=DirectoryZ&utm_medium=PaidLinks&utm_campaign=FooterLinks The traffic would then be tracked accurately and you can see it in the campaigns report.

There are a couple tactics you could try: See if http://archive.org/web/web.php has a cache of the page. Use OSE, Majestic, etc to find backlinks to the page. Maybe one of the backlinks will include a description of what was on the page.