Is my analysis of TI TL431 schematic correct?

[annebrt]

1. The schematic (taken from the TI TL431's datasheet) is divided into three blocks as in the image: block 1 is a band gap reference, block 2 is a differential pair, and block 3 is a Darlington configuration. Is it correct?
2. If my division is incorrect, how to divide it? If my division is correct, why is it still a valid differential pair since the left and right branches are not symmetrical? What is the impact of the asymmetry?
3. What is the function of Q1? What if connect directly without Q1?

 

[jms_embedded]

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