Case law

I see a lot of VBA employees on here that claim they discount medical opinions of "claim shark" companies. There is no regulation or law that allows the VBA to discount a medical opinion from a competent medical provider. Also, the veteran paying for a nexus is not wrong according to any law or regulation. The veterans board of appeals noted that no medical service or opinion is provided pro bono. So my question is this... Why does the VBA ignore laws and regulations by ignoring a nexus from a competent medical provider when there is case law established against that?

https://www.va.gov/vetapp20/files3/a20003992.txt