Oxy,
I guess u r more experienced than me so your question surprise me , anyway I try to answer your question.
In up-trend we expect that price will retrace but will not break mid band & Visa-versa in down-trend, it is normally expected that it wont..how-ever this is pre assumed theory..it should not but it can.
U know well the stock market follow jungle rules as anything could be happen..
Here is a chart of adlabs..u can check the price continuation at upper band as-well it did not break the mid band from 11 to 12.30+ 3 to 3.30 PM and letter on from 1 to 3 pm the price continuation was either at lower band or below mid band.
Cactus, I do not intend to post as an authority,but to derive rules from Bollinger bands, one must first understand why the bands are used. With the assumption that prices are normally distributed, Mr.Bollinger induced that 99% of the items would fall within 3 standard deviation from the average. The outliers, if any would eventually fall back into the bands, and hence, considered mean reverting.
Without understanding of assumptions, one is making the primary mistake of theorizing from examples. IMO, this sort of understanding will leading to more confusion than solve any. The set of "pre-assumptions" as you state are merely a reflection of "what you want to see" rather than what is? Perhaps I am mistaken here but I guess it's upto to either of us to rectify it.