Um, if you have 8 pages of journal entries, you would have 8 "new" flips your first time through, then 7 each time after. Thats because you aren't opening it onto a new page, you are starting from a previously used page. Try your math with this info included and see how you go.
I would assume thats where you went wrong.
But didn't it say that he had 8 pages with a caught/defeated Poke, then 1 that didn't? If so, then he would have 8 pages each time, since he starts on one that doesn't count.
Y-Y-Y-Y-Y-Y-Y-Y-N-Y-Y-Y-Y-Y-Y-Y-Y-N
Y= yes, advances RNG
N= no, does not advance