1. Had the whistle blown
2. Were investigated
3. Had enough evidence found during the investigation
4. Were fined successfully
5. Were announced via the SEC whistleblower program
Nobody knows the dropoff at every stage but it's certainly non-zero and so we can't judge the level of crime based on the number we know coming out at stage 5.
I don't think it's overly cynical to assume that 278 is a small percentage of the actual count of financial crimes in the US since 2012.