|ã€zero in dateã€‘
On the blog which you show, the author says "CWT32(12/15ã€16ï¼‰".
CWT = Comic World Taiwan, a doujin convention in Taiwan.
There's a map on the page (CWT32 æ´»å‹•è³‡è¨Š) and it says ä¿ºä¼éµ joined both 12/15 and 12/16.
So the release date must be 12/15.
"12/6" on the page inside the book must be the date when the author wrote that page. I don't own the book but I guess it's postscript or something, isn't it?
In most cases, release date is printed on colophon.