He was with God before anything was made. It was just Him and God so no need for names. He seems to have remained without name until He was made incarnate 2000 years ago in Bethlehem. He was till then described by prophets who saw Him in visions but no name mentioned. He then had to be born and live growing up as human among other humans who saw Him as like anyone else though a bit surprising at times in what He did and said and so at last He needed a name to identify Him among the masses and even just among His earthly family. Fitting that the name be imparted by angels who had known Him as Lord and Son of Man and Son of God and knew His glory. It is there in a couple of ancient prophesies known today but partly obscured by the wear and tear of the ages that the name of Him was made known long before His coming in the flesh. Enoch prophesied but it is a prophesy now with some fragments lost. The name of this Son of Man, he apparently wrote, had been revealed to the angels to help them counter evil but it is not clear whether this meant a name as we mean by a personal name or whether it is an invocation of His reputation or title. Isaiah had a hint given him that the child to be born as a salvation would be named (personal name) like his own name which was a sign of it (obscurely hinted at in Isaiah 8) and indeed the names are very similar in some languages and have the same meaning. Otherwise The Christ and The Almighty are similar in revealing that they need no personal name and can be believed to just exist anyway irrespective of any personal name. They are - whether or not they have a personal name. The need for a personal name to distinguish one among many is associated with being merely one among many. Although the Son of Man became like that, He is also unique and without anyone besides Him except the Father who too is unique. There are not several 'Fathers' in the way that God is Father. There are not others exactly like the Son of Man. Neither necessarily need personal names. Each can say simply "I am".
