Final answer:
Broker-dealers must record all unresolved security differences to maintain accurate records and meet regulatory requirements. These include discrepancies in trade orders and actual transactions.
Step-by-step explanation:
A Broker-Dealer (BD) must record on its books and records all unresolved security differences. This requirement is important for ensuring accurate record-keeping and accountability in financial transactions. Unresolved differences might include discrepancies in trading, where there is a mismatch in the details of a buy or sell order, and the actual transaction recorded. These differences should be identified, documented, and diligently pursued until they are resolved to maintain integrity in the financial markets. It is a regulatory requirement for BDs to maintain such records which are subject to review by regulatory bodies like the Securities and Exchange Commission (SEC).