Board Thread:Lore Discussion/@comment-17114085-20140120134645/@comment-4705438-20140120155524

Songs of the Return also state that Ysgramor build Windhelm. We don't really know what was the governing system of Atmora. Previous rulers in Windhelm, twelve before Harald, were also considered kings.

So in addition to the Falmer and Dragons Ysgramor Dynasty also had to fight Reachmen. King Harald was first to unify the territory that we now know as Skyrim. Kingdom exited before him, but he finally conquered Skyrim as a whole.

So in the end it all comes to your definition. Ysgramor Dynasty lasted ever since he built Windhelm. The expanded Skyrim existed since High-King Harald and lasted about 200 years.

Also, note: Pages tend to be flawed, look up sources for valid info. Pages usually have them. Also, feel free to make the corrections if you see that they are needed.