Backlink Data From a Historical Perspective
A website's link profile is dynamic - new links emerge and old ones fade away. That's just the way it goes in SEO.
Knowing which links are dead, however, provides an opportunity to get them back and thus improve the overall backlink profile.
Unfortunately, there have not been very many solutions that provide the ability to collect this historical look at backlink data - but they do exist and ahrefs.com, a very popular SEO tool, is one of them and has just released this functionality last week.
Ahrefs begain collecting historical data on Aug. 13, and now offers two indices - "fresh" and "live."
The Live index contains links that were live on the last re-crawl, whereas the Fresh index contains the links that the solution has seen as "live" starting on that date (including those that were dead on the last re-crawl).
There are, of course, many reasons why link counts go up or down (e.g. hosting server downtime, DNS issues, etc.) but simply because a page/link was "down" does not guarantee that it is in the current moment (as they may be back online).
For that reason, Ahrefs.com also introduced a new column in its Site Explorer tool called "Backlink Status," which provides more details on the status of dead backlinks - "not found" (because of one of the reasons listed above), "removed" (where the page was OK but the backlink was not found), and "dropped" (where the page and link exist, but the quality is low and Ahrefs won't include it in its report).