Kasumi Shigefusa material differences

I have owned two Shigefusa kasumi gyutos in my life. My first one was very thick at the spine, heavy, stiff, and the cladding was very soft and discolored easily and immediately. This second one is a good bit thinner, much lighter, somewhat bendable (not Takeda bendable, by any means, but somewhat), and the cladding is tougher and doesn't discolor nearly as readily. The construction and fit and finish is essentially identical, and the core steel seems exactly the same. The cladding seems very similar to my new Heiji carbon gyuto, unlike my first, and presumably older, Shig. Is this a known thing, and I'm just behind the times?

My Shig - one of the recent, thinner ones - doesn't react on the cladding as easily as I'd read it would prior to owning it. Just seems normal in that regard. It is somewhat bendable.

jacob, i acid etched that blade, which might explain the difference? this thing was super reactive when i first got it. i didn't know that was the thinner lighter incarnation however. what about the height? i felt it was a little narrow.

Ah, the acid etch would explain it! After refinishing, I noticed that it was picking up more readily, but not the way my old Shig did. It's about 50mm, and I'd guess it was about 52 when new. I like 50. A friend recently bought a 240 Kitaeji, and it was 52mm, OOTB.

Shigefusa has told me that the core material is also different between his suminagashi and kasumi-yaki pieces. It is possible that he has also changed cladding materials over time.