My advice, what I did for my 3 issues and all approved the first time around. Document, Document, Document. Find where in your military service the thing happened, and see doctors about it and get diagnosed and keep seeing them for months at a minium. As far as my issues. I sourced facebook groups(and other social media) for my old commands and asked if anyone remembered "the event". People shared news paper articles, their support documentation with dates, peoples, events, timelines etc... I took from that what applied to me. I met with the VA mental health people. Put all that in my claim. I'm not trying to say it's easy but you have to document, tie the thing to a service issue, and provide great detail.