First, here's a material that made me keep thinking about this issue in the first place.
http://www.grammaring.com/as-if-as-though
She acted as if she didn't know me.
It was the first time that I'd seen her since I was in elemantary school.(and now I'm 26). A couple of days ago, when I met her, she acted as if she didn't know me. I think she didn't remember me.
She acted as if she hadn't known me.
I broke up with her a couple of weeks ago, and when I met her yesterday, she acted as if she hadn't known me. She definitely knew who I am, but pretended as if he hadn't known me because she didn't want to talk to me.
Is it right that I make a situation like that with each sentence? I hope this try will be concerned not only for me, but also for other English learners.