Emergency call works slightly differently to normal calls, in particular, it could start with the phone completely disconnected from the tower. So specifically

Emergency call works slightly differently to normal calls, in particular, it could start with the phone completely disconnected from the tower. So specifically emergency call being available in 2G doesn’t mean the phone still registers on 2G. It’s probably a legal requirement that if 2G is supported emergency calls on 2G must be also supported. Maybe there are some LTE-3G dualmode phones without GSM in the world, if that’s what you must have?