That explains it. Blackstone is incapable of accurately measuring fuel dilution and have shown an inability to properly measure viscosity as well.
I would disagree to some extent. But only on the merit of your word choices.
I don't think Blackstone is "incapable". They make choices for certain equipment and costs, etc. The flash-cup method is not very accurate; I'll agree with that. Their viscosity equipment isn't sub-standard; it's reasonably accurate. They, however, don't use the formal vis ranges in their reports; they use their own ranges for vis (essentially an "should be around this" approach which can result in confusion, admittedly). I'm not a fan of that, but that does not mean they are incapable of accurately measuring vis.
What I learned of my tour at BS many years ago is that they are heavily dependent upon human interaction with the test methods. In gauge R&R speak, the "reproduceability" factor is probably not as robust as we'd all like it to be.
It's not that they aren't capable of being more accurate; it's a matter of the test processes being subject to human variability. I suspect that the inaccuracy you object to isn't a result of being "incapable", but more a factor of not being as precise due to factors involving humans. Poor performance isn't always a result of incapability but perhaps moresoe that of inattention, distraction, timing, low give-a-crap factor, etc.
The net effect may be wanting for more, admittedly. I'm just delineating the difference between capability and other reasons why accuracy may be less than desirable.
For someone like me, who really doesn't care about vis or FP much, those tests which are highly dependent upon human process interaction don't really affect my patronage. I care most about the wear metals and other elements, and the ICP process they use is reasonably trustworthy.
If vis and FP accuracy are paramount to one's lab choice, there are other labs that offer more suitable choices.