Technorati’s index seems to be rather forgetful: it does not find blog posts older than six months. Frankly, I don’t know if it’s a new “feature”, or it’s always been like this, and I’m just the last person to notice it.
The only time-limit I’m aware of is calculating Authority, which is based on the revolving 6-month link-counts, but I haven’t found any reference in Technorati’s FAQ to the “shelf-life” of posts in their main index. I’ve only done limited testing, but if indeed this is the case, then Technorati is toast. There’s a lot of value in old posts, and the index that finds them is not Technorati, but Google.