Good point. You can bet it wasn't a junk mailer.
Personally, I'm satisfied with the assumption that the J-Lo letter was the source. Which makes the "soapy powder" an important clue. Obviously something was added to "cut" the spores and bulk them up. Something that invited touching and smelling.
And I recall the one piece of hard information we've gotten about the chemical testing of the spores -- they incorporated "a surprising ingredient". Some kind of detergent or surfactant...or a fabric softener, with its anti-static properties?