It had been previously assumed that River's story was the inverse of the Doctor's. It now seems we have a different shape - that of the umbrella. Imagine an old style umbrella in a stand. The tip of the umbrella is silence in the library and as we move up we have the likes of Flesh and Stone. Move further up and the 'tip' of the umbrella comes alongside. This is 'Demons Run'. We see the start of Melody Pond along with an older River.
Move further up along the handle of the umbrella and we have 'Let's kill Hitler'.
This opens the intriguing possibility that we don't know if we're on the shaft of the brolly, or the handle on a given occasion in a future episode when River appears. Will we see the newly born River, who only knows Mel and 'Let's Kill Hitler'? --- who has been researching the doctor in Luna U - and who possibly is still shaking off her programming .... or will it be the older, more experienced, River - who has yet to visit the Doctor at the end of Demon's Run?
Could we see both at once?
What will happen as we reach the 'inversion point' at the top of the umbrella?
Caveat: This picture is somewhat simplified as we know that the doctor revisits ‘The Impossible Astronaut’.