I've done a lot of reading and listening to what adopters want from 'the book' but suppose where I get stuck is why is the book THE important bit. It can't ever be, it's a moment in time however well it is done, no SW knows what that child will need as they grow up. The story is the thing and that's got to be for adopters to work out with their child, who they will know better than I ever will.
Sorry it took so long to get back to you! Like you I know that the book however good is a snapshot of that moment in time and cannot respond to the needs of the child. Ideally Adopters should take the time to equip themselves to develop the life story with the child in a natural and unforced way when it comes up. That said the book can be a starting point and should be as good as possible. Bad examples abound unfortunately.