Square Enix Members and Square Enix Account Management are two separate things. SE Members is for all their games library, and the "no games registered" has to do with those little red and white slips of paper that come in all SE games, the ones that come with a code you can redeem for points.

SE Account Management is for XI and XIV accounts where you can manage your subs, redeem XI or XIV codes, etc. The correct link you want is here.

Aside from that, you can't register any codes right now, so sit tight and keep watching the Lodestone for announcements. We will be able to register the pre-order codes on the 20th.