I want to repeat that while transparency is a virtue for agile teams, not all agile teams may be there yet. While perhaps keeping the results of their next few retrospectives private, those teams can work on feeling more comfortable opening up in the future.
This is a good post from Mike Cohn that points out that you can’t just flip a switch and be agile. Culture changes take time. You can’t force a team to be transparent just as you can’t tell them how to self-organize. They have to chose to do it on their own. What you can do is encourage a team to be transparent, help create an environment where they feel safe, coach leadership on their feedback and interactions with the teams, and lead by example. Poke, prod, nudge, question, and challenge, but always allow the team to make the decision, don’t make it for them.