Your point of residual metals of the previous fill might be valid. I do believe the cleansing refers mostly to removal of organic contaminants like acid, soot, water, etc. than the non-organic contaminants like wear metals. But I would think the lab would be able to trend and identify when the oil becomes saturated and loses it's ability to hold the wear metals. Also, you should be able to tell with a decrease in count of the additives magnesium and calcium that the oil no longer has the ability to remove, hold and suspend the contaminants which would lead to residuals left behind during an oil change.
I would also have to consider the SAE studies that I pointed to earlier to holding a lot if weight in this subject. It is one thing to look at an oil sample, but to get a better point of view, look at the actual parts in questioned for actual wear rates.


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