Sandy, thanks for you comments. I wondered about two minute after bath in the used developer. However, decided to go that route not having any other information. Thornton used it with Exactol Lux so I decided to try it too.
I cannot attest to the same CI on the different developers as I do not have a densitometer. I do remember in Thornton's writings that he too found too Exactol Lux to print faster, "thinner negatives." He, I believe, attributed it to the amount and color of the stain. The film was all exposed the same, all on the same roll, motor drive, etc.
Incidently, some years ago when XP2 came on the scene I exposed a roll at 50, 100, 200, 400 and 800, both of grey card and of the same scene. All the negatives printed the same, same paper grade and the prints looked almost identical except with slight increases in grain at each end of the speed spectrum. The densitometer plotted all the curves as identical just shifted up or down depending upon the film base coloration. Printing times changed correspondingly, of course. Interesting.