Apologies in advance if this was already reported/responded to (I thought I had reported it long ago).
The CheckUser logs currently date back to December 2006, while CheckUser as a user right in its current logged form dates back to June 2005. Prior to December 2006, the CheckUser broke entirely and the entire log up to that point went with it. This is true across all projects. Ideally, we should restore the missing log entries from that first year and a half of CheckUser. The record of these log entries still exists, they just need to be added to the log visible on the projects. I have the missing logs in a text file on my computer, but since that was sent to me by Tim, I assume it can be retrieved by developers somehow.