When inputting /testfor @a[c=2] with only one player online, a true output is still given with a SuccessCount of 1
Reason this is a bug: The test is incomplete as there are not at least 2 players online, yet there is still a true output given.
Comparators should only output signal strengths after the argument has been met. If c=10 and there are 10 players online, output a signal strength of 1 (from a comparator) and if there are 24 players online, output a strength of 14.
The c parameter limits itself to the amount of results, it can be lower, not higher.