You are very correct about FINRA having a hard time keeping track of Naked Short Selling, just read the PR's about brokers getting fined. hint: it took years for FINRA to realize what happened!
FINRA Fines Cantor Fitzgerald $2 Million for Regulation SHO Violations and Supervisory Failures:
As a result, Cantor did not timely close-out at least 4,879 fails-to-deliver, and routed and/or executed thousands of short orders in those securities without first borrowing (or arranging to borrow) the security or issuing notice of the need for a pre-borrow to the broker-dealers for whom it cleared and settled trades.
FINRA Fines Merrill Lynch a Total of $6 Million for Reg SHO Violations and Supervisory Failures:
Merrill Lynch's supervisory systems and procedures were inadequate and improperly permitted the firm to allocate fail-to-deliver positions to the firm's broker-dealer clients based solely on each client's short position without regard to which clients caused or contributed to Merrill Lynch's fail-to-deliver position.