only after/ only when/ not until

[tranlam1609]

Are these four sentences all correct?
I only recognized him when he came into the room.
It was only after he came into the room that I recognized him.
It was only when he came into the room that I recognized him.
It was not until he came into the room that I recognized him.

Do they have the same meaning? If possible, please tell me the differences.
Thank you.

 

[Raymott]

Yes, they are all correct and all mean the same.

 

[Matthew Wai]

'I did not recognize him until he came into the room.'
Does it mean the same too?

 

[Charlie Bernstein]

'I did not recognize him until he came into the room.'
Does it mean the same too?

Yes.

But how could you recognize him before he came into the room?

 

[MikeNewYork]

He/she could have seen him before that in the hallway.