From what I remember, Yurdrain is a gifted name from Katchian, who was emperor at the time for becoming the cavalry commander, but I'm just remembering off the top of my head so I'm not too sure. I vaguely remember it because Kishiar mentioned that Yurdrain meant beginning and end or eternity in an ancient language and said it was a was a well-thought out name/title.
They’re talking about when kishiar stepped down as the commander of the Calvary and gave the position to yuder, which happened a few years after forming the Calvary. There was a ceremony and that’s where yuder was given the name yurdrain as a gift for his new position. If you want more detail I can look for the chapter talking about it, sorry if I didn’t make sense I tried my best to explain it.
I'm at ch 301 and I don't remember if it was mentioned so I'll just ask here, why isn't Yuder's name Yudrain in his second life? I read back to the earlier chapters and it seems that, that's just the name he was born with, so how did this change in name occur?