Having the pre-order items doesn't require having the expansion. They're based just on the pre-order code and not the expansion code. The pre-order code alone would also have allowed you to play Heavensward content from the 19th through the 26th. It was only as of this last Saturday (the 27th) that they started requiring the actual expansion code in order to access HW.

None of that explains why your account isn't seeing the expansion code if you'd already registered it, though.

What platform are you on? (Only asking because the process for registering the codes is different between computer versions and console versions.)