You’re right Brian, when I said oil tempered, I meant it in type 98 oil tempered, so differentially tempered. The 95, I believe are through tempered in oil or water. As such, they don’t have a nioi temper line.
Chris, I think the 98s are in their majority differentially tempered. Now, it doesn’t mean they didn’t experiment and I wouldn’t me surprised if some were spring tempered with an etched Hamon added. It could have been an experiment like gensuito. A spring tempered blade is very resilient (at least, modern ones are!) and we know that they were making experiment to make better gunto, so that’s not out of the realm of possibilities. Then again, the blade you’re showing seems to show a real Hamon, especially in the kissaki, so who knows?
Besides, there seems to be a discrepancy in the transition between the Boshi and the Ji. I think the real Hamon is closer to the ha and the hazy Hamon goes higher than the nioiguchi.