Deleting old completed orders

Client is on Sage 300 v2023, but now has many years of history.  Using OE Periodic Processing > Clear History > Transaction History, 79 out of about 50,000 orders are left behind within the date range selected.  All lines are marked as Complete, and the Order status is Complete/Day End (COMPLETE = 5).  The Delete button on these orders is grayed out.  The Tairox "Delete Orders" utility does not override Sage's limitations here.  What would prevent some orders from being deleted?

Thanks in advance,

-Wendy