The four questions
Which records produced this figure, and can I see them? What population does it cover, and what does it exclude? How was it calculated, and can it be reproduced? What did the work not test?
A number that survives all four is defensible in front of a regulator, a counterparty or a court. A number that fails one of them will not.
PERISCOPE briefings describe investigative principles. They do not disclose detection logic, thresholds, formulas, weighting or rules.