I had this question as well. The Early Access instruction document contains this line:
You will be notified via email prior to the launch of the game on when you can return and redeem your preorder code to unlock Early Access to the game
However, the order confirmation email contained "Serial Numbers". The purchase history page at the online store contains the same information with no mention of Preorder codes. The use of different nouns introduces ambiguity: Are Preorder codes and Serial Numbers the same? I needed clarification (because it is not a good idea to not know and just hope) so I got in touch with support through the contact form at store.na.square-enix.com.
Here was my question, exactly as submitted:
The information provided after completing my purchase
includes two "Serial Number"s. However, the additional instructions
state that it will be necessary to enter a "Preorder Code"s. Are the two
serial numbers I received for my two collector editions the preorder
codes? If not, how might I obtain them? Thank you.
The answer I received today began like this:
Thank you for contacting the Square Enix online store.
Your serial numbers are: ...
Please note that serial numbers, registration numbers, unlock codes and
passwords are usually case sensitive and if they are not entered
correctly, you will be unable to activate the program.
My query was either not read or understood as the reply is clearly inappropriate,
but the canned response does mention "serial numbers", "registration numbers" and
"unlock codes", an indication those are distinct things. But what of
Anyway, I've submitted another inquiry.
Does anyone here already know the answer to this question?