Thanks for all your thoughts and information, it is helpful. I think ultimately what you said about beginners needing more information is correct. If you are asking a beginner “not to clamp, instead change your shape”, then the best teaching it to explicitly teach what this means so that it can be internalized by the learner. Once it is internalized (because the learner knows what it feels like and doesn’t feel like, looks like and doesn’t look like), then the learner can stop thinking about the lips and “think about the music, how it sounds, what the conductor is doing, or the band or other performers, etc” as you have mentioned.
Otherwise, bad habits are formed.
I try using the questions that you have provided as I play. I am still thinking that a beginner could answer yes to these questions without realizing they are actually clamping their lips.