All coaches are utilized until the end of their codal life. The RB is very particular that no rolling stock (locos, wagons, coaches etc) should be put out of use before the end of the codal life under any condition, unless they are damaged beyond repair (like accidents etc).
Long ago, the RB issues orders to the effect that even at the end of the codal life, rolling stock should be decommissioned only if it does not meet safety standards.