The TBN drop over that many miles is not big issue, IMO. Insolubles are still low (considering the miles). Fuel dilution was low. Metals were very low. Yeah, this oil could do 10K. Looking at this UOA, I'm not sure I would want to go past that without scrutinizing another couple of reports, but 10K is OK, IMO. I see nothing wrong with wringing the last bit of additive out of the oil... it's good until it's not! It's all about the amount of drop. For all we know, that oil will hold at TBN 1.7 for another 3K miles. Some oils have a high initial number and drop precipitously and others have a lower starting number but drop lower.
Everybody remember that when reading a Blackstone UOA, for whatever reason, their TBN reads lower than every other lab I've seen. That's why they will run it down to TBN 1 and other labs will not. The only way to judge is to have them run a VOA on the same oil. The TBN on the VOA will also read lower. Example: I have a VOA where the TBN reads 8.5 but the manufacturer lists 10. Now, the mfrs numbers will vary slightly from batch to batch (mfr tolerances and all that) but if you know that on the scale of the lab you are using from, going down from 8.5 to 1.7 is not as big a drop as 10 down to 1.7. You can argue that [censored] is inconsistent but they are consistently inconsistent. Their TBN numbers can be judged against themselves.
