Not sure which knife has which treatment.

Through hardened is when the entire piece of steel has the same temper/heat treatment. Differentially hardened is when they make main portion of the steel spring tempered so it has more flex and won't snap as easily and the edge part of the blade is harder to hold an edge better.

I would imagine any of the waki type blades would need to be dif. harden, but I am no metallurgist or anything.