Notice that XTOL is well above 8.20. I thought my meter was reading high, but I did a two-point calibration, and it passes the Borax-test. Methinks that Kodak boosted the pH a little after filing the patent.
Ryuji, when testing DS-10, you noticed that some 100-speed films develop poorly below pH 8.2. I suspect that Kodak observed the same thing late in the game, and boosted pH to give themselves more pH-headroom. Either that or my meter's defective.
As far as I know, Kodak never changed the pH of XTOL. pH of 8.20 and 8.37 would require serious adjustment in development time.
But you are using single junction gel-filled electrode, so I am not sure how trustworthy your measurements are.