I believe if you check Gen. 4:26, you will find that men began to call on the Name of YHWH. Likely these were men only from the line of Seth and Enosh (since Cain's line was definitely self-absorbed). It may be both a name and title, because after all, this is the Holy One the Creator of Heaven and Earth, the Rescuer of souls...There is no other.
Nobody knows what they called Him. Moses wrote Genesis well after that and He set the standard since he met God on Mt. Sinai and was given His name then.