Just curious how you know he's only using white #1 now--product description says "High carbon steel core laminated with Gokunan-tetsu." Reading that, I figured it was something different since he didn't mention the specific steel.
It's pretty common for smiths in Japan to just focus on 1 steel in order to come as close to perfection as possible. It was maybe about a year ago in a newsletter that Murray stated that upon reflection of what he thought that it would take to further improve his craft, he decided to take inspiration from some of his mentors and dedicate himself to one steel.
He did have and existing stock of blue super (AS) that he said he would continue to make knives from, but once it was all gone he wasn't buying more. I guess that it's possible that he still has some old AS kicking around, I just didn't think that it was likely.
I really loved his use of AS and thought that the slight trade off in maximum crazy sharpness and ease of sharpening wasn't bad for the extra toughness and edge retention, but I understand his mindset as he's not really about "trade off's" and is all about attaining maximum sharpness/ cutting performance as quickly an easily as possible and white #1 is what he feels best lends itself to that purpose.
Still, we're talking in pretty esoteric and hair-splitting levels of difference and as much as we all would like to look tough behind our keyboards and claim that we can tell the difference, between the 2 steels, I think that very few of us actually can.
Bottom line is that if there's a "Carter" stamp, then the steel stamp really doesn't matter for anything beyond our own Knerdy curiosities. It's gonna get really sharp, really easily, and cut really well.
EDIT: just poked around the site a bit, and I was surprised to see that he recently posted a batch of stainless-clad AS knives; so I guess he still does have some left. It's been a really long time since I've seen KU iron clad knives in AS from him, but I guess it's still possible.