The Enforcement Policy concept that's missing from this discussion is "cross tolerance."
The TILA and Reg. Z set the standards for APR and FC precision. Anything outside these limits is a violation and causes civil liability under Sec. 130(a) of the TILA. If you want total protection from lawsuits, you must "take the cure" spelled out in Sec. 130(b)--including full reimbursement. Sec. 130(b) does not tell you how to compute the amount of reimbursement, however.
Enforcement actions are a different source of risk. Regulators do not create liability, they force you to protect yourself from it by taking the cure. They tell you how to compute the amount of reimbursement via APRWIN.
Recognizing various arguments about the effects of tolerances, the regulators provide more leeway than the TILA. This includes the ability to compute the dollar-equivalent of the APR tolerance for a loan and use it as an additional FC tolerance. (The same applies in reverse, but the % equivalent of the FC tolerance rarely produces a more favorable APR tolerance than the ones in the Regulation.)
Think about it--an eighth or quarter of a point in a long term loan is worth A LOT MORE than $100.
APRWIN has this Enforcement Policy feature built in. It doesn't tell you how much the "bonus" FC tolerance is, but computes and uses it to determine whether a FC reimbursement is necessary.
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...gone fishing.