Date is on the last line before signatures. 12/26/1986.
My bad. I stopped at the end of the list and was looking at the top for the date.
MMM1?
Amazon?
Marvelous Middos Machine Episode 1, the album the song being quoted is from. Amazon lists the original release date as March 5, 1984 on the product page.
Not sure I get why you asked which is older, but it seemed like you though the letter was older.