Thank you for the questions! I’ll start answering these now; though, it will likely take some time and discussion to address them all.
You asked first, “Does BANA ever recommend including the math text without annotations before introducing the annotated text?”
The example you shared implies that what you mean by “annotations” is things like carried numbers, omissions, etc.
I cannot point to any place where BANA or ICEB addresses the possibility of brailling a math expression twice (once without certain aspects and then a second time with all printed aspects included). So, we do not have official guidance right now.
Personally, I would NOT recommend transcribing the math without its full work/calculation. If you wanted to clarify for the reader what is the core expression, you might include a short transcriber’s note to say so. (e.g., The worked example shown below is 42×36.)
–Kyle
P.S. I am still working on your other questions.