There are two notification dates to consider, the one given that may be within the 60-day threshold and the one that may be outside the 60-day threshold. Each uses different considerations.
For Billing Error consideration, the notification date is the date the financial institution received notice (Tuesday per your example). If that date falls within the 60-day threshold, use Tuesday as your date to calculate all provisional credits.
Any transaction that falls outside the 60-day window from the above date would then qualify for 205.6. Under that section your time frame starts from the date that the consumer provided notice (Saturday). The fact you got the notice in-house 3 calendar days later does not impact this notification date. The regulation is specific that the consumer does not have to contact the number/address provided and the notice does not have to actually be received in order to be valid.
205.6.b.5 Notice to financial institution. (i) Notice to a financial institution is given when a consumer takes steps reasonably necessary to provide the institution with the pertinent information, whether or not a particular employee or agent of the institution actually receives the information.
You might have to back date some credits and issue an interest credit depending on what transactions qualify given the time frame requirements.
The staff commentary on section 205.6 gives some great insight into how to interpret consumer notification.
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