Yes, you must provide the notice but you cannot deny based on credit score. Your denial must state the reasons pertaining to the factors that caused the score to be low.
As far as where it is found. You would need to read the definitions of "adverse action," "application," and "completed application" under 202.2. And then read the section about notifications at 202.9.
If the customer applied for pre-qualfications and you say "no," it's an adverse action event.
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The more you sweat in training, the less you bleed in battle.......