There is no Exposure Time in Category A operations.
'The reliability programme of aircraft in operation and maintenance is a combination of statistic monitoring and recording of the events associated with the airworthiness of an aircraft. The results obtained by monitoring reliability in operation may serve as a basis for supplementing or modifying the aircraft maintenance programme; such changes would indicate the malfunction of components or systems manifesting lacks and the need for early control, or replacement during utilization.'
https://www.maintworld.com/R-D/Aircr...lity-Programme
Any failure of a tail-rotor in a larger aircraft results in a challenge to the pilot - as you have seen from experiences shared on other threads.
Helicopters are certificated on an understanding that they will meet the projected reliability rates. If they do not, it is for the Airworthiness Authority to establish a route to rectification. This can result in amendment to maintenance procedures but cannot mitigate the event that causes the review.
JimL