I could swear there was a rule that said if the Lith secret/achievement card was revealed, then it was no good anymore. I seem to remember it being discussed as a strategy to reveal them when I was annoyed at the power of a few of the special cards.
Of course, I can find no such rule. Has my poor mind completely fabricated the rule or is it somewhere in the rule books and I missed it?
I believe that it has been stated on these forums that they are useless once revealed, but by useless it was meant that the other player would never let you complete it.