The problem with titles

As the plethora of poems with such illuminating titles as 'Untitled' or 'Sonnet' seems to suggest, coming up with a title constitutes something of a struggle for even the most hardened of poets. Paradoxically, I've been suffering from the opposite problem of late - loads of titles have been suggesting themselves but with no poem to go with them. Hence the blank or only partially filled spaces where 'Blues for my Home Town', 'Snail Weather', 'The Comfort of Railway Stations', 'Are you Sure you Want to do that?' and 'Gestures of Independence on Dogger Bank' might be. I'm not complaining. I'm just intrigued. Did Ashbery think of 'Self-portrait in a Convex Mirror' before he wrote the poem or afterwards?