Character name-appearance withot explanation

[Guest]

I am reading the sixth volume, and i am wondering, at chapter 14, the character "Death Gun" (earlier described as "Sterben"-in game name, from begining until now) becomes "Steven" as Kirito speaks of him)...is this a translation error?
"sterben" is first introduced in chapter 9, and this character name is the same until chapter 13, where kirito uses the name "steven" instead of "sterben". Asuna explains the "misspell" sterben-steven first in chapter 14. For someone who reads it the first time (like me), ive got confused, why suddenly "steven" instead of "sterben". Also, is it possible, that two persons translated the same volume, and one of them used the term "sterben" until chapter 13, and the other continued with "steven" at chapter 13. kirito used the name "steven" without explaining them one chapter before Asuna explains it, so why?