You're right that you can't always wait for the evidence to make a decision. I think that part of what you have to do is weigh the existing evidence and make your decision based on that and based on the fact of somebody being a veteran and having served their country.
To use the example of the depleted Agent Orange, the studies that came out of the U.S. were on people who actually had Agent Orange dumped on them, not those who were just in the vicinity of Agent Orange. With Agent Orange it's actually graduated on level of exposure, and unless Canadians were serving with the American military during Vietnam, there weren't really any who had that kind of exposure.
That's where I mean that the evidence is critically important as you make the decision. You may still find in favour of that veteran, and I would certainly never say that anything should win out over anything else, but it's really critical to look at the evidence carefully.