Formerly secret, and perhaps extrapolating (surely for N > 0 discovered cases, there are M > 0 still secret cases, since it seems unlikely to have a 100% reveal

Formerly secret, and perhaps extrapolating (surely for N > 0 discovered cases, there are M > 0 still secret cases, since it seems unlikely to have a 100% reveal rate). And "large numbers" is highly subjective in this case. It would be reasonable to consider two to be a high number for something so surprising.