Thanks for this, Leigh. I'm going to make it a sticky, and move it into the Rules Forum.
(But please, everyone, feel free to discuss it here.)
We've addresed this before, but no one can be expected to read, much less remember, all our discussions. I think a good rule for a discussion board -- at least this one

-- is that any PUBLIC performance, which could include a master class or an open rehearsal -- can be commented upon. But if it's a private rehearsal open to donors, or "friends," or if you get in because you know a dancer, or are family, etc. I think it's better not to comment, for all the reasons Leigh has mentioned. Also, if what's posted causes a problem, the person who smuggled you into the rehearsal could get in trouble -- and you may not get invited back!
In the future, posts about private rehearsals and classes will be edited to delete that material, and the poster (gently) notified