If you're in the Facebook Nihonto group you can message the guy. I believe his name is Raymond Yan, I'm sure he would be up front about what he thinks they are(or are not). Just a thought.
Sorry if this isn't the answer you're expecting, but that seller(Eric) is quite informed and prices accordingly. Most likely blade is market value based off it's quality plus dealer markup. In short, I doubt Eric is looking to hoodwink anybody this is his business.
On this link Bruce seems to have compiled that same stamp multiple times. Referring to it as wrapped steel method. Seems they've all been found on only Kaneshige blades.