I've gotten confused over the years about where TBN condemnation points should really be. Some labs go for 35% of initial value, some go for TBN/TAN intersection. According to a Honda paper, 1.0 is the point past which wear starts increasing. However, Blackstone is way off the mark in telling people that this is sufficient. As important as TBN is oxidation over a long interval. Higher oxidation is first going to show up as deposits. First at the pistons, which isn't going to show up in a UOA. When comparing M1 and PP/PU, I saw some UOA's where TBN still measured 1.0-2.0 but Pennzoil showed signs of oxidation in the form of significant viscosity thickening, yet Blackstone was happy to tell the user to push on. Thankfully most who do extended oci's do use some kind of M1 that seems to have better oxidative stability than just about anything else.