Generally, I'd say the official unofficial policy on name changes is that from an IC perspective, they can be considered retroactive. That is, once you, the player, know that Monte Cristo was once named High Guard, your characters all know that the character was always named Monte Cristo, and everything that High Guard did, they know was actually done by Monte Cristo.
This is because name changes are not an IC tool to change your RP or escape from a bad rep; they are an OOC tool to change bad/inappropriate names into good/appropriate ones.
On the other hand foreign nobility are foreign nobility, and the particulars of their lives and true names may or may not be known further afield - especially to latter generations.
Merlin: STAND BACK! Be silent! Be still!
Merlin: That's it... and look upon this moment. Savor it! Rejoice with great gladness! Great gladness! Remember it always, for you are joined by it. You are One, under the stars. Remember it well, then... this night, this great victory. So that in the years ahead, you can say, 'I was there that night, with Arthur, the King!' For it is the doom of men that they forget.
