Did you know that the criteria being used today to evaluate a patient for Alzheimer's are the same ones suggested in 1984. They were proposed by the organizations which were the predecessors to the National Institute of Neurological Disorders and Stroke an the Alzheimer's Association. I was actually surprised to realize that 29 years later, we've not evolved our criteria significantly.
In 2011, new guidelines were proposed at the Alzheimer's Association International Conference in a public workshop. The summary of the workshop is Alzheimer's Diagnostic Guideline Validation: Exploration of Next Steps.
It is actually an interesting and relatively short read. The summary discusses the challenges for implementing a new set of guidelines. The biggest of which is answering the question of "how soon is too soon to treat?" The criteria will be evolving as scientists and doctors work to answer this and other questions.