He had glimpsed the Supermind in 1908. But that is not the same as reaching. In a letter of 1920 he writes to his brother that he has risen to the lowest of the three levels of the Supermind. Of course he was also working upon the world which makes it more difficult. He started writing Savitri in 1916. But this is true of his inner being, of his soul, if you like. But then it is necessary for the nature, even the outer nature of which the spoken and the written word are clear indicators to also rise to the same level.
A simple analogy will help understand the difference. Imagine someone has an idea that it is possible to fly or to create light from the electric power available in the world. This idea might come from a high, a very high source or plane of consciousness. Many scientific ideas, especially in the previous century came like that. But for the idea to actually manifest in the outer physical plane using the brain cells and the outer materials normally needs several trials and attempts. So too while one may glimpse something of the Divine in some deepest inmost state not many can express it because the instrument is not ready. But as one goes about expressing, the instruments begin to accomodate. They shed their resistances and can express the higher truths more and more freely and with a great freedom and plasticity. It is only then that one has truly and fully ascended. Otherwise it is like taking a flight to the highest in Samadhi but a return to the same old bodily house with all the old habits and difficulties.
Affectionately,
Alok Da
