Clearly just dealing with one demon should count as a handful of difficulties. One minute Tang Seng falls into the water, that's a difficulty. The next minute the four disciples are starving, that's another one. Tang Seng hasn't even left the Great Tang's borders, and it's nearly ten difficulties already. But by the time they'd finished fetching the scriptures from the Western Heaven and tallied up the difficulties, dammit—how is it still missing one?
In that era when Saints concealed themselves, Tathagata was already the pinnacle of the immortals in the mortal world. Can't he count from one to eighty-one?
It's just that he couldn't be bothered.
Anyway, no matter if this was done perfectly or not, I've already arranged it for you. Nobody can nitpick, and nobody dares to say it was done wrong.