Did you have a chance to see the original book? Maybe you were expecting too much if you didn't see the 1st edition.
Also, this can be the case (option 2):
Sam Sloan (who now owns rights to some old Ishi Press books) scanned an English 1st book edition,
worked a little bit on it and then print it out.
He didn't use high quality scanner / high dpi, and didn't bother to pay someone who knows a little
bit about publishing & PDF manipulation (assuming it was PDF), so the result is not so good image quality.
I own several (originally Japanese) books reprinted by 'all done in my kitchen and spare time '
(better word would be illegal) Chinese "publishers", and the quality vary from very bad to not bad/acceptable.
The price is several times lower then the originals, so can't complain much.
But some (illegal?) publisher are making new diagrams & text (eg, redoing books totally) and publishing high quality books.
Like this one from Taiwan. https://goo.gl/cbTDTk
His edition of Improve Your Strength at Go 1 & 2 by Segoe Kensaku cost around $11 US (fraction of the originals) and looks great.
BTW, I've checked mine The Breakthrough to Shodan, Kiseido Digital Books PDF edition.
It's 300 dpi, greyscale (screenshot below) but printout is not bad.
I’m wondering did Ishi Press use it? (note added: Based on your description they didn't as it looked fine when I printed couple of pages
(also, this PDF can be changed to black and white, cleaned and made it even better for printed book if someone wants to go that route)
All above reminded me of the English translation of All About Life and Death 1 & 2 by Cho Chikun.
I am 100 % sure that Ishi Press (different publishing company from this presently owned by Sam Sloan)
copied the original books, and then cut & glued diagrams into English text.. If you look at the books (if you own them)
you will notice how diagrams are positioned under the angle, and then letters 'a', 'b' , ... inside the diagrams are also angled.
That's because they glued letters 'a', 'b', 'c' over existing 'イ' , 'ロ' , 'ハ' (used in the original book).
That was the fast and easy way, and still much better looking then some Yutopian older books (where diagrams where printed on dot matrix printer and used in books).
I hope I didn't hijack your thread by writing about other stuff as well.