There is some conflicting data with different versions and roles.
On one hand either the last or 2nd last Mk was considered inaccurate and wore out quickly. OTOH the same guns served around the world in shore batteries for 50 years and was considered accurate falling in a ballistic sweet spot.
I don't know. 100 years of confused sources.
The 9.2" was very accurate when it was a new gun being fired, but a worn gun was very inaccurate due to the high velocity of the weapon, causing increased dispersion. Shore batteries often fired lighter shells or reduced charges for practice, so that might contribute to their longer life.