I still note no one actually uses Khan's full name except for Spock Prime which felt like a backdoor out for the writers incase they changed their mind about his identity.
They didn't use his full name in TWOK either and it was still Khan. I mean really how many times does ones full name come up in conversation anyway.
When one is specifically asked who they are as they were in the film? If someone asked who you were you wouldn't just shout your first name and leave it at that. "WHO ARE YOU?" "JOE!"
And the TWOK example isn't the same situation. My comment wasn't meant to imply it wasn't Khan, but rather a weird evasion of the longer name, which might be grounds to be played with in a tie-in comic. The Spock scene almost seems like "Huh, we never did get the whole name in there."