Emily Skillings, in her intro to the Ashbery book, ways that he would grade the poems in a projected book, A, B, or C, or with some pluses and minuses I guess. The finished book would consist of A and B poems. He would even have others grade for him, like the poet and art critic John Yau. A B poem might still add a needed element to the collection, by complementing other poems, without being brilliant in and of itself.
I felt a sense of warm affection and admiration for Ashbery from Skilling's introduction. It seems very genuine to me. I got a different sense of his work, too, from these unfinished projects, something more charming and quirky, more forgiving.
I've done this myself, with translations. I give them grades and then work to get the C translations to a B level, and the Bs to A, etc... Or course, since we are grading ourselves, we have no choice but to be honest, because there is no point in giving ourselves all As. The point is to be able to see what is good and not, and why. Grading someone else is punitive, but we have to be able to perceive our own work on some level.
On facebook people were talking about their distaste for bad poetry, and I thought, well, most of us write bad poetry, after all, including most participating in the thread, probably. We have to exempt ourselves from the category of bad poetry just to write at all, to claim something of the art for ourselves. We have to have a happy relation to our own art, even if an A+ poem by me would be a D for Ashbery.