Studies on memory show that human beings, as a whole, are terrible at remembering things. We edit, we re-write, we create. Almost certainly some event you remember clearly from more than 20 years ago either did not happen at all, happened to someone else and you heard about it, or happened in a completely different way than you remember. That's true for just about everyone[0].
What good is a device that can tell if you believe you're telling the truth when your beliefs and memories are so flaky anyways?
[0] Except my wife, whose near-eidetic memory is frightening.