I'm almost certain that Kuhn would not publish an essay with grammatical mistakes, but those two sentences seem plain wrong to me. (I am not a native speaker.)
Though my argument does demand that I illustrate them briefly, my views will begin to depart from those long current only after I have done so.
The last part of this sentence sounds just wrong to my ears.
My critic asserts, however, that there is only one such value of p, that corresponding to objective choice, and he believes that all rational members of the group must arrive at it.
In my opinion the third comma needs to be removed and an "is" needs to be inserted after the second "that".