E.214 GT composed of CC+NC+MSIN used in AUTH triplets request in LU callflow. Also used in USSD-requests in roaming.
E.164 GT composed of CC+NDC used in almost all other SCCP-based callflows. SMS exchange for example.
E.212 GT – IMSI. I’v never seen it used for something. But opened it on router (just in case).