Well, I was doing quite well in chemistry through inorganic, qualitative and quantitative analyses and chemical engineering lab. I have found that the only thing of real value that one learns in school after the basics, which I new before I went to school anyway, is how to learn more. I do know cations and cathodes and anions and anodes and a lot of other things. There is NO mention of potassium on that page under that heading or any other. Lithium, calcium, sodium and ammonia are discussed but not potassium. If you want to come look at my book, I'll get you a bottle of some really good local wine and we can go over it together. My copy was printed in 1969.
I reread the chapter on procesing after development beginning on p.397 and ending on p.407 in my 1969 edition. I found three references to potassium. The first was the one about adding some KI to the fixing bath speeding up washing.
The second was on p.401:
"Strauss found that sodium chloride acts as a fixing accelerator whereas sodium bromide has some retarding effect, although Sheppard & Mees found that 0.1 M potassium bromide had no effect on rate of fixation."
The third was on p 402:
"Where potassium alum is used as a gelatin-hardening agent in an acid hardening fixing bath, the retention of argentothiosulfate ions is greater."
I do not mean to imply that you are wrong, but that I had at my disposal no means of proving one way or the other. It is pretty obvious that my edition is not the same as yours.
I cannot imagine what borax would be used for in an acid hardening fixing bath. Boric acid I could see, but the culprit here was potassium alum, presumably in much greater quantities than any that might come in with impure sodium tetraborate.
It is also pretty obvious that my edition came out before the TMAX series.