See FinCEN's The SAR Activity Review Issue 8, 2005.https://www.fincen.gov/news_room/rp/files/sar_tti_08.pdf
"For situations where the nature of the activity reported changes after the original Suspicious Activity Report filing, the suspicious activity is no longer considered “ongoing”--e.g., the customer in the above example begins sending or receiving funds in addition to making structured withdrawals. In such cases, the institution should consider the changed activity a new transaction and should file a new Suspicious Activity Report within the normal filing deadlines, rather than updating a previous filing after 90 days. Because the activity is related, however, it may be appropriate to cross-reference any previously filed Suspicious Activity Reports in the narrative. Further, if previously reported activity ceases, no further Suspicious Activity Reports need to be filed."
Rather than filing multiple parallel SARs, you can combine structuring with the new activity, but don't wait the 90 days from your previous filing. You have 30 days from identifying the new transaction pattern to file you SAR.
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