In 2013 VHA explained to me their policy which reversed the decision first reached in 2001
The Agent Orange Registry is fully detailed in VA Handbook 1302.01(Agent Orange Registry Program) dated 5 September 2006, except for the changes ordered by Post Deployment Health that relate to C-123 veterans.
The confusion arises because the veteran seeking an Agent Orange exam must, of course, believe he or she has been exposed. It seems the logic, by decision of Post Deployment Health, is that no C-123 veterans were ever exposed. That apparently is the reason for orders to VAMCs to deny C-123 veterans any such exams or health care. No possibility of exposure = no AO exam. Simple.
I hope this clears us the confusion we caused by reading the regulations and VA's web site, which don't include the VHA decision.