I had learned it at the last meeting

[keannu]

I think one-tense-prior rule is not that strict, so "had learned" here can be replaced by "learned" only, right?

gz45)I didn't laugh at the joke because I had learned it at the last meeting.

[Barb_D]

... had heard, not had learned.

You could use simple past, but the past perfect sounds more natural to me.