Recently, I discovered that when the Rav Kook was sick before he died, a third name was added to his name - Yechizkiyahu. This can be seen in this sign calling to people to pray for him:
and in some of the newspapers reporting on his passing. See here for example, pg. 2.
However, in other places, the name is never used. It isn't even on his tombstone:
Most people, to my knowledge, aren't even aware of this third name. Is it known why it was not used after his passing, in particular not inscribed on his tombstone?