a. She didn't know that one of my friends was a policeman.
b. She didn't know that two of my friends were policemen.
Is it possible that I had other friends who were policemen but she knew about them?
In that case the sentences would sort of be ambiguous.
In one case, I had only one friend/two friends who were policemen.
In the other case, I had more but they just didn't know about one or two of them.
The reason I have two example sentences is that I think when we have 'one of my friends', we can replace it with 'a certain friend of mine' (that would make the friend more specific). With other numbers that option does not exist (maybe one could go for 'two specific friends of mine' but I think that would probably sound odd and won't help matters.
The idea is that I have a few friends who are policemen, but she doesn't know about one/two of th