The Canadian site
getyourdrugstested.com seems to have the same testing parameters, however they have found isopropylbenzylamine
eleven times since February 2021, all around the Vancouver area. They completed around five hundred methamphetamine sample tests in that same period, so I think the only conclusion we can accurately come to is that n-iso is rare ( ~ 2% ) amongst people who lab-test their twack.
This could be a representative sample of the whole tweaker community, or it's possible that those who have their gear tested are a self-censoring group due to bulk buys, greater health concerns, a higher sensitivity to cutting compounds, etc., but we can't determine any of that.
The only thing we can know for certain is that n-iso is out there and generally at 100% of the tested sample. I encourage everyone in Canada to test their suspected n-iso cut gear at this lab. It's free, and donations of any amount are accepted and would probably make them very happy.