When I bought the key from Kinguin and entered the code into Mog Station, there was a fine print that mentioned "Early Access ends on 27 June. Please ensure you enter your registration code by then to continue playing." or something in that line.

So I'm wondering, the 20 digit code that Kinguin gave me is just for early access+pre-order items? I have to buy the actual game as well to have access to the actual registration code that comes with the game?

Not sure I understand your question right but what I meant in my previous post was if we need to buy a physical copy of Heavensward to play the expansion beyond the early access period. Or Kinguin will provide an additional code to us when Heavensward is released. Because my understanding is the 20 digit code it gave us are for early access. Unless I'm sorely mistaken, I did not see where was it stated that this code will also be used to digitally download the expansion when it's out.

Sorry if my question sounded really idiotic. I just need to make sure.