I think that the possibility that he is from Canada or another country other than the US is lessened by the fact that he knew the postal abbreviation for Idaho. For instance, I wouldn't know the Canadian postal code for Saskatchewan or any other provinces.
It's unusual that he did not include the zip code with his address. He appeared to fill out the fourm exactly as specified, writing down only his name, address, and state. I know that out of habit, I would automatically write my entire address, including city and zip code because they seem to go as a unit.
Was this a sign that Lyle was thinking very concretely, as many with severe psychiatric illnesses (in this case major depression) do? Or was he accustomed to following orders (eg military) or paying strict attention to detail (eg scientist or accountant)? Or perhaps he was simply trying not to draw attention to himself, providing only the information that was requested of him.
The SUICIDE paper is also interesting, in that the writing appears different than the others. It is more exact in this instance, with each letter separated and distinct. Like he wanted it to be very, very clear.