Board Thread:Lore Discussion/@comment-24267938-20130323172448/@comment-4258298-20130323185227

Septim Dragonborn =/= Dovahkinn Dragonborn.

It has been state that when the emperors are said to be "Dragonborn" it is refering to their connection to Akatosh (Other than Tiber Septim, who was, of course, Dovahkinn). This connection is portrayed through Martin 's ascension as an avatar to Akatosh. Therefore being Dovahkinn (having the soul of a dragon) is not the same as having a connection to Akatosh and being royally "Dragonborn."