Commentary to 226.6(a)(2)(10) states: When creditors use an initial rate that is not calculated using the index or formula for later rate adjustments, the initial disclosure statement should reflect: (1) The initial rate (expressed as a periodic rate and a corresponding annual percentage rate), together with a statement of how long it will remain in effect; (2) the current rate that would have been applied using the index or formula (also expressed as a periodic rate and a corresponding annual percentage rate); and (3) the other variable-rate information required by footnote 12 to ยง 226.6(a)(2).
Footnote 12 info [when rate may increase, limitations on increase etc] needs to be included on the initial disclosure stmt. I would not use an addendum. I would disclose the teaser rate and "regular" rate in the same area of the disclosure. The early disclosure must state that the initial rate is discounted and how long the discount will be in effect. (plus other variable rate disclosures) Info in the table (early disclosure) must reflect the discounted rate.
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Opinions are my own and not of my employer.