The interagency enforcement policy establishes a "cross tolerance" that neither exists in Reg. Z nor Section 130 of TILA. All of the regulators calculation tools were designed to apply that additional tolerance--but only for the purpose of calculating amounts the regulators will make you reimburse. If you're defending a lawsuit or are trying to eliminate civil liability, Section 130 requires you to reimburse any understatement. If you're dealing with an investor, you might be held to the Section 130 standard, or the more generous Reg. Z standard. If you're dealing with your regulator, the Policy Statement will apply.
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...gone fishing.