My mum donated her brain for Parkinson's research; the report was quite short and very much in medical language, but did confirm the diagnosis of Parkinson's and Lewy Body Dementia, but also mentioned Alzheimer's, which hadn't been diagnosed previously.
I phoned the Brain Bank for a slightly more "layman's" explanation which helped, and Googled some of it too.
But the key thing for me was the confirmation of the diagnosis, along with confirmation of suspected TIAs which showed up as tissue damage but couldn't be confirmed whilst alive, but which we suspected had occurred due to sudden marked declines over time.