A Stripe export with repeated headers, decimal separators that swap convention mid-file and customers whose emails differ only in case. Esan cleans it, splits the quarter's churn between the customers who left and the ones who downgraded, and proves the split against an MRR bridge that closes to zero. Then it reports what it found on the way: one of those duplicate emails is not a duplicate, and the company behind it has been paying for two plans since January.