Lesson 3 is I think confirmed. Communication around the SMP introduction, and the well-known differences of opinion which surrounded it,  2  BIS central bankers’ speeches  tended somewhat to undermine the coherence of communication by central bankers generally and was, I would say, problematic.
The jury is still out on whether the policy has been a lasting success, and there are of course different views on what it could have been expected to achieve long-term.