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I've learned that if I get signs that today is not the day to do something, I find something else to do.

Haha. Yes I've made 7/8 razors that were going to be 8/8's :)
Knifemakers don't make mistakes, they make smaller knives.

For a knife of that type, I would leave 1/2" of hardened steel. 4 ish mm is not enough, considering that there is a huge amount of non hardened steel applying force to it.
The good thing though is...

Scott's using differential heat treatment to create a hamon. You want water quench for that in order to get sharp hardening lines.

Btw, how wide is the hardened part? If it is narrow, there is going to be a lot of stress on a very thin piece of steel.

A couple of questions. Did you smoothen out the edge before HT?
I also notice the the knives are curve upwards significantly. Did you make them like that, or is that the result of the differential...