Unless I missed something, all VA disability payments are for service connected conditions. If it's not service connected, the VA awards no disability percentage for it.
This is correct, but only to a point. The operative terminology is a "nexus" demonstrating a connection between the claimed disability and military service during specified periods. In addition to simple and common sense applications (such as demonstrated physical injuries incurred on active duty) there are dozens of presumptive associations.
Type II diabetes is accepted as presumptive evidence of exposure to Agent Orange for those who served in Vietnam while that chemical was in use.
COPD may be considered presumptive for those claiming exposure to burn pits where contaminated items were destroyed during Desert Storm and other campaigns.
PTSD is treated as a presumptive issue for anyone who served in combat units during specified periods.
Tinnitus is presumed and benefits routinely awarded for anyone who served during qualified periods, even though there is no definitive testing to verify the condition. Simply filing the claim is usually sufficient to be awarded ~10% disability.
In addition to the presumptive tests, a nexus may be established by a claimed aggravation of an earlier service-connected issue by later events in life. Many examples can be given, but generally speaking just about anyone who served in combat arms assignments (infantry, airborne, etc) who later experiences limitations in joint movements and/or arthritis problems may be granted disability pensions even though many years may have passed.
Alcoholism and drug addition issues are frequently used to pursue disability claims, the nexus being cited as "young, dumb, scared to death, readily available", etc, etc, etc.
This discussion might go on forever, but suffice it to say that the current bureaucratic position seems to be granting disability claims on even the most questionable "nexus" rather than being held accountable for denying anyone applying. Dozens of nationwide law firms have built thriving practices on nothing more than assisting in filing claims and contesting every adverse ruling (all for a small percentage, of course).
Additionally, means testing (income & assets) have all but been eliminated in disability pension cases. Disability payments are treated as an earned benefit. Not unusual to see people pursuing full-time employment and careers with substantial salaries while also drawing VA disability payments.
Perhaps you can understand why I choose to dance around the differences between truly service-connected disability awards and a routine practice of granting pensions to just about every doper and alcoholic loser who steps up.