The churn among 9 year customers is miniscule and, to the extent it happens, is largely out of your control.
(They've successfully resisted all temptation to quit for NINE YEARS. Crikey, your commercial relationship is already more stable than many marriages . Typical events precipitating a cancellation sound less like "Found a better deal" and more like "I'm moving outside your service area" or "Dear Comcast: Dad died, please cancel his subscription.")
Thus, offering 100% of 9-year customers a discount to influence a fraction of a sliver of those customers (the number who are seriously considering cancellation who could be motivated to not cancel if they were offered a better price) is just throwing money away.