Your disclosure must be correct at the time it is given, so I believe you need to revise it on a go forward basis. I don't see anything that would require you to notify existing customers of the change. Nevertheless, my personal decision would be to notify them via statement messages without regard to the time frame established in the regulation for mandatory notification.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.