Original Message

(b) and (d) work together to establish rest requirements (not duty limits).   You are limited to 8 hours of FLIGHT TIME per day and it must be planned to be earn where you can show 10 hours of rest in the preceding 24 hours.   You can't plan to fly any flights (under Part 135) after that 14th hour of DUTY, but you can certainly remain on duty beyond 14 hours since (b) and (d) are not duty limitations.

(c) was created to provide an exception to get a higher flight time taking advantage of regular circadian cycles, which is why it restricts the duty under (c) to 14 hours.   You cannot exceed 14 hours of duty under (c) because it will interfere with the body's circidian cycles of rest, which will interfere with flying more than 8 hours.   

Under (c), since you have regurlar duty periods established of no more then 14 hours chronically, the FAA provided an exception to increase your flight time limit from 8 to 10 per day.   Even regional airline jockeys don't fly 8 hours per day normally in airplanes.   Maybe some GOM operations would benefit from (c), but certainly not any HAA operations.