The most important thing is to get in the queue. I applied for SSDI and it took 4 and 1/2 years before I got it. I agree, you are going to have to describe symptoms rather than diagnoses, if the doctors haven't nailed that down yet. Of course, it's better to have something concrete, something that can be demonstrated.

For me, the hearing officer relied on a 3DMRI/MRA performed by Dr. James Collins at UCLA and on an MRI done by Dr. Scott Werden in SF. My attorney had to make copies of documents in the court's file and we could see where the hearing officer highlighted those test results. He also noted them in his comments during the hearing.

If you start the ball rolling, you'll likely have time to develop better facts (in the way of diagnoses) before you come to hearing because the process is so darn slow.