tmn111

“What I'm confused about is, how to call it, something like "pure" past perfect with no any conditionals, phrases with "wish" etc.”

Have you followed that link I gave earlier?

tmn111

“

We were good friends. We had known each other for years.

Could I say in this situation: We didn't know knew each other for years?

”

Yes (as corrected), but note that the present viewpoint statement is:

We are good friends.  We have known each other for years.  ("perfect of the present")

The most logical way to transfer this into the past viewpoint is as follows:

We were good friends.  We had known each other for years.  ("perfect of the past")

Remember that the past perfect is a dependent tense.  It connects with a past point of view established by other statements referring to past time.  It makes the past perfect statement seem more like an explanation of the simple past statement.  If you use We knew each other for years you don't connect the thought as strongly with the previous statement that you were good friends.  It seems like another independent statement not necessarily related to the fact that you were good friends.

Similar situations where the past perfect is in some way explanatory of the previous statement in the past:

Marty was ecstatic when I saw him yesterday.  He had won the lottery.
Lucy looked very tired last Monday.  She hadn't slept well the night before.
Helen was not very excited about seeing "Gone With the Wind".  She had already seen it three times.

CJ