so i've done some research on this question here's what i've found
prior to the VCAA
a veteran had to have a diagnosis for the claimed disability and the va had no obligation to help them get one without the veteran first proving the claim was well grounded which sent a lot of veterans through a bizarre maze where they needed a diagnosis but couldn't see a doctor. the VCAA makes it clear that the VA is now suppose to help you get to see a doctor to get a diagnosis after you file the claim.
so it is true that you have to have a diagnosis for the claimed service connected disability,
it is also trough though if you don't have a diagnosis you can file the claim and ask the va to assist you in getting an exam with a doctor to get a diagnosis.
this is what my research has come up with.
the law 38 U.S.C.S. §§ 1110, 1131.
below if from The Veterans Benefits Manual 2007 edition and they explain it better than me i think.
"Before November 2000, when the VCAA was enacted, veterans had to obtain a medical diagnosis of a current disability on their own. The VA was not generally obligated to help them in obtaining this medical evidence. 110 Some veterans, who could not afford a private doctor, were placed in a no win situation. They could not receive disability compensation until they submitted a medical diagnosis of their current disability; they could not get the VA to provide them with a free medical examination to obtain this diagnosis because veterans who already had service-connected disabilities were more likely to receive free VA medical care; and they could not obtain a medical diagnosis from a private doctor because they could not afford to pay for the private doctor.
As a result of the VCAA, most veterans who file an original claim for disability compensation do not need to obtain a medical diagnosis on their own. 111 The VA is generally obligated to provide veterans with a VA medical examination to diagnose the current medical condition. There are only a few legitimate reasons for which VA may refuse to schedule a VA medical examination." Veterans Benefits Manual