Clearly, Cloudchaser is her actual name, Stormwalker (Dark Lord of All) is what she’s trying to get everypony to call her.

So both cloudchaser and stormwalker are both official

Cloudchaser was the name they used in the cartoon, but that was only because there was no model for cloudchaser, so they used Stormwalkers model instead

@RIG  
Don’t make me hit you with the super slowpoke stick, RIG.  
You can read the whole thing here.

@RIG  
Cloudchaser was her fanon name, Stormwalker was attributed in some official works.
 
Honestly, I just put them together, like Lyra Heartstrings.
 
Cloudchaser Stormwalker.  
Probably one of the most awesome names I’ve heard.

what? who is stormwalker? i thought their canon names where Flitter and Cloudchaser.

Omg!