My background reading on the late Yeats poems drew me to the CK Stead book, The New Poetic: Yeats to Eliot. Here I discovered an interesting perspective on the ‘meaning’ of poetry, derived from Eliot’s literary criticism (and clearly, informing his own poetry). Stead says:

‘For Eliot, as for Yeats, a poem is to be tested not by what it says but by what it is… Eliot, like Yeats, has been concerned to achieve something more positive than the aesthete’s Beauty; and less deceptive than the rhetorician’s Truth… by means of a developing critical theory and poetic practice which give equal weight to a “structure” provided by the positive rational will, and a “texture” which is the gift of the negative imagination.’
CK Stead, the New Poetic: Yeats to Eliot, page 126

Eliot himself has these things to say about the poetic process:

‘… the mind of the mature poet differs from that of the immature one not precisely in any valuation of “personality”, not necessarily being more interesting, or having “more to say”, but rather by being a more finely perfected medium in which special, or very varied, feelings are at liberty to enter into new combinations.’
TS Eliot, Tradition and the Individual Talent

According to his perspective, even the author might not be aware of the meaning of his or her work:

‘All good poetry contains much that is strange even to its author. Its imagery draws on memories which may have symbolic value, but of what we cannot tell, for they come to represent the depths of feeling into which we cannot peer.’
TS Eliot, Charles Eliot Norton Lectures

One final quote reveals much about the creative process, at least for Eliot:

‘In a poem which is neither didactic nor narrative, and not animated by any other social purpose, the poet may be concerned solely with expressing in verse – using all of his resources of words, with their history, their connotations, their music – this obscure impulse. He does not know what he has to say until he has said it… He is oppressed by a burden which he must bring to birth in order to obtain relief… he is haunted by demon against which he feels powerless, because in its first manifestation it has no face, no name, nothing: and the words, the poem he makes, are a kind of… exorcism of this demon. He is going to all that trouble, not in order to communicate with anyone, but to gain relief from acute discomfort; and when the words are finally arranged in the right way-or what he comes to accept as the best arrangement he can find-he may experience a moment of exhaustion, of appeasement, of absolution, and of something very near annihilation, which is in itself indescribable.’
TS Eliot, Lecture to the National Book League, 1953