How can you tell a first printing of Tokyo Ghoul?
Japanese tankōbon carry a colophon (奥付) at the back: a block of small type giving the title, author, publisher, the issue date and the printing number. A first printing says so there, in the form 第1刷発行 (first printing, issued) with its date. Later printings increment the number while the book otherwise looks the same.
Two consequences matter for Tokyo Ghoul. First, the ISBN does not change between printings of a Shueisha volume, so an ISBN can identify an edition but never a first printing. Second, the issue date in a first printing’s colophon sits close to, but not always exactly on, the release date: volume 1 was released February 17, 2012, and its first-printing colophon is the document to check against that date. Belly bands (obi) are supporting evidence only: they were printed for the season of release, so an obi advertising the 2014 anime on an early volume already marks a later printing.