Bug check fee sql

modules/purchase_trade/docs_source/business/sql/README.md

@@ -71,6 +71,11 @@ For every other fee, it recomputes the expected quantity from the effective
 - `lot.qt.hist.quantity` for net fees and `lot.qt.hist.gross_quantity` for gross
   fees.
 
+The diagnostic is grouped by `fee_id`. Purchase and sale columns are displayed
+only to help identify related contracts; they do not split the expected
+quantity. This matters for purchase fees whose linked lots may also be matched
+to several sale lines.
+
 Run it on a restored test database:
 
 ```sql