No, I meant Action, not Action card, because that's what Conspirator refers to. So like, when you play King's Court - Conspirator (1) - Conspirator (2) - Conspirator (3), the Conspirator (2) will activate because that's your third Action that turn, even though it's your second Action card.
It's not your second Action card, though. It's your third. First was King's Court, second was Conspirator (1), third was Conspirator (2). At least that's how I'd see it.. Conspirator doesn't say Action (or Action card) in play, it says 'played'.
You can't play the 'Actions' that are considered in Diadem because those are counters, not things that get played.
Conspirator (1) and Conspirator (2) are the same card, so they are the same Action card. So what is Conspirator counting? I think it must be:
Number of the times during the turn you either
1) Played an Action card by spending an action from your action pool; or
2) Played an Action card as a result of being instructed to do so by some effect (like Throne Room, Procession, King's Court, Golem, Herald, and Cultist).
I remembed Donald saying before that if he had a do-over on Conspirator, he would word it like Peddler to count Action cards in play.