I've read a lot of suicide notes in my life, or rather, I haven't. By definition, the suicidal people who come to my hospital are ones who survived the attempt. The ones I see are going to be heavily weighted toward those who at least partly, somewhere, ambivalently wanted to live. And yet there are circumstances where people do survive by ridiculous accident, and if they have previously left a suicide note, you can treat it as authentic. All the notes have some authenticity in them. It is rare to see one that is entirely gestural and attention-seeking. All of us have mixed motives in everything we do and try to raise the good motives and lower the selfish ones as best we can.
You learn quickly about suicide notes, as about later self-justifications, that people are not reliably truthful. Sometimes they do not know their own motives, sometimes they wish that their statements were true, sometimes they flat out lie.
I thought of this when someone in a comment section linked to the story of the lesbian couple who had the many mixed race adoptive children, who drove off a cliff with the lot of them. Notice that the article is slanted sympathetically, that the story that they had had a cross burned in their yard by some Minnesota KKK-style group was possible - even likely, they hint. Well, they're from the UK for openers, so unlikeliness of a KKK in Minnesota of enough size to risk going out even in darkness and lighting up a cross in someone's yard isn't that surprising.
In the discussion, someone angrily wrote "If they knew they were about to kill themselves, what motive would they have to lie about a thing like that?" I thought of the suicide notes. It's not reliably the time when people lie least; for many, it is the time they lie most.