TBN? TBN is ok, when its ok. How poor was it?
I self don't know better or worse TBN. TBN is "reserve". If you have reserve, you have reserve. 4, 3 or 1.68... its reserve

Its furthemore all good, if you have fruthemore reserve. For me the oil shall not "retention" TBN. TBN have to work (imho)
Wear more or less ok, but stay in grade for 40?
https://www.2addicts.com/forums/showthread.php?p=22545925
In my buddies BMW Alpina B3 S Biturbo (N54B30) it was after 9.400 miles a 0W-30 (11.70). NewLife was 9.200 miles later, on 13.15.
Now M1 0W-40 is no more NewLife and primarily, no more Venom

I also don't like it, not anymore. I had love Venom.
Castrol 0W-30 is one of a better 0W-30. For 0W-40 its no longer applicable.
Do it. Its ok

This oil will be not take blow up the engine. Its not the best, but also not catastrophic decision.
But
extol Castrol 0W-40, now, it will be no one oil-nerd understand in the EU. We were quite pis... with Castrol, as we find out (in expensive spectra analyses) that the base oils are worse than before (with equate prices) and Castrol pump their best base oils
now mostle to 0W-30 (504 & Co.) and 508 oils.
Not its GropuIII and are also very sensitive for fuel discharge. IMHO (own observations auf UOAs) double sensitive than before.
No, thanks, Use it. Keep it.
edit:
All of this, imho. This is not academic analysis nor of course
stand up in court stuff