I have three extracts:
A: Do you know this man?
B: Yes, I had met him before war, but I haven't seen him since that time.
A: Is he a student?
B: Yes, he studies at our university. He worked at our university. He worked at our factory before he entered the university. He isn't working any longer.
A: Where does he work?
B: He isn't working now. He's a student. He worked at our factory before he entered the university.
Once I posted the first sentences having asked about the acceptability of using Past Perfect in that context. The answer was that
"war" isn't a
"reference time", so that I had to use Past Simple in the examples 2 and 3, meaning that
"working" was a habitual action that is no longer valid.
But what does
"reference time" mean?