The pre-order codes being sent will depend on where you bought from and when you ordered. They started sending them awhile ago depending on vendor, I was reading this and hadn't received mine either and I bought from Amazon, which was one that was reported as sending codes out quickly. I emailed them and they told me they had already sent the code a good two weeks prior so they forwarded the email again with the code and I got it that time. It was odd.
As for the pre-order registering for early access with the code, that I want to say they said will be starting on the 20th, although they also said when you register your email on the pre-order page that they would email you specifically with the info.
I'm a bit confused. I'm about to pre-order but I'm not sure how this works. So there are two codes a pre-order code given by teh vendor and then a pre-order code fore registering (given by SE). But then, what is this: http://preorder.na.finalfantasyxiv.com/us since they just ask your e-mail, can I just put my e-mail and get a pre-order code? I'm kindda lost with this :/