How does Shopify account for Refunds with empty transactions?

[Bill6]

I am trying to match Shopify's "Sales Over Time" report and how it calculates the daily refund totals.  I am finding discrepancies are often related to Refund objects with empty "Transactions[]" but still containing "refund_line_item" arrays with refunded items.

Sometimes Shopify will include these "refund_line_item" subtotals on refunds with no transactions.  Sometimes it doesn't!  

Does anyone know the basis Shopify uses for including "refund_line_item" subtotals when there are no Transactions[]"?  Also, why would Shopify ever include refunds with empty Transaction arrays?