Hey there! This has been one busy week, but I finally got to translate this thing. Back when Kaitai Yoeko DVD was released, about one year ago, I wrote a post to announce that one of the attached bonus of it would be a last letter from Yoeko with a serial number. I just realized this post I wrote is still a draft that I never published, damn it!!
By the way, so yes, there was a letter inside it with a serial number that was written right before SHUUGAKUSHOU was released, around September, 2008. It was translated by me, that means it's not an accurate translation, but it's a nice reading for all the fans.