At the end of this episode,
when Rory and Amy are taken by the weeping angel, the Doctor realizes the last page of the book is an afterword written by saying they lived a long happy life. However, River says before this that the Doctor will never be able to see them again.
What I am confused about is, if the author of this book had prior knowledge of what would happen when they wrote it (as seems apparent early in the episode), then why
wouldn't/couldn't she, in the afterward, simply write something like "by the way, after the angel took me, it sent me to location X at time Y, if you want to come pick us up". Even if they had no way of knowing where/when they were sent, it seems from the rest of the episode that reading an event from the book made that event a real fixed point (i.e. the portion Amy reads about River breaking her wrist), so by writing it there and then reading it, wouldn't the Doctor have been able to go to that time and place and find them? I guess I'm confused why all the other details of what happened are in the book but they couldn't put where they end up.
There seems to be another possible solution as well:
Since their gravestones are in New York, with their real names, it seems very likely that there is some sort of record of them in public records, including where they lived and when. It doesn't seem like it would be too hard for the Doctor and River to track them down this way either. Why can't they?
Also, for the record I'm only at that episode in the series, so there could very well be something in future episodes that explains it (in which case please refrain from giving it away).