1 and 2 are OK. 3 and 4 should be "I've known".
Do you even know her name? I say:
Can you say this :
I knew her name the whole time.
I've known her name the whole time.
I knew her name since we first met.
I've know her name since we first met.
Are all okay?
MikeNewYork, I don't understand No.3 is needed to add "I've known", why I knew is wrong?