Not so much an oversight, more like all these references have yet to be addressed. Afterall, NPCs like Sharven and Jayose are still Xacha. Many players are still Xacha. At some point there's going to be a switchover. But all references to Xacha will have to be changed in books, quests, knowledge areas, etc. ... anywhere there is such references. That hasn't even begun yet, but it will at some point.