Acc. to a Russian lab the VO of a Castrol Magnatec A5/B5 has :
TBN 11.62 mgKOH/g per ASTM D2896(ACEA A5/B5 limit is min.8mgKOH/g; max.1.6wt.% SA )
Si 8 ppm
Concerning the by-products (by oxidation,nitration,sulfation) here are two old write-ups worth reading:https://www.machinerylubrication.com/Read/561/oil-analysis-diesel-enginehttps://www.machinerylubrication.com/Read/873/oil-tests
As for diesels you'll see varying condemnation limits among manufacturers (even the warning levels vary with labs). I'd definitely shorten the oil change interval and would be happy if the soot loading is kept under 1wt%.
Check if the intake system is sealed.