The theory ...
Inputs matter the most. FP, Vis, TBN/TAN, elements all are in the oil and speak to the health of the oil. In theory, watching these vigorously will assure a good running engine.
The reality ...
This UOA shows wear rates are reasonable and no signficiant contamination is present.
Case closed.
The reality explained ...
Inputs are just that; they are only individual criteria that go into a formula which results in an equation.
Ouputs are what matter most; what is the result of that equation.
Don't worry about inputs as long as the output is desirable.
If you have good wear, why does vis or FP or TBN matter? IT DOESN'T !!!
The inputs are only predictors to what MIGHT happen, yet outputs are telling you what actually happened.
You can know the starting roster of a basketball team, and know it's seed in the tournament, but the final score tells you who won. And at times, the "inputs" can be misleading, inconclusive, or inaccurate.
There are scads of examples where TBN was low, but wear rates continued to be fine.
There are scads of examples where FP was low, but wear was fine.
There are scads of examples where Vis was low, but wear was fine.
There are plenty of examples where wear was bad, but oil health was great.
The point? If there is no correlation between the characteristic and the output, then there can be no causation of effect.
We've seen countless examples of TBN/TAN crossover, and conventional wisdom from decades ago said "gotta change oil when the crossover occurs". But that was just a prediction based on a suspected result, and NOT based on an actual result.
There are three kinds of PM practiced when maintaining equipment:
1) "Preventative Maintenance" means you're changing something (lubricant or part) based on a prescribed schedule, often just a guess which has shown to be effective, but not necessaryily maximized for efficiency
2) "Predictive Maintenance" means you're looking at data that speaks directly to some rate of performance, and some rate of failure, balancing the two for safe operation AND efficienct management
3) "Panic Maintenance" means you just run it until it breaks, and then suffer the downtime costs
- Changing oil based on some distance (every 5k miles) is preventative, but not predictive. Changing oil based on inputs (X ppm of Ca; Vis at Y cSt; FP at Z deg C) is also all preventative; you're not looking at what's happening to the engine, but only viewing the oil.
- Changing oil based on outputs (wear rate levels and trends) is predictive, because you are tracking results of what's actually happening in the crankcase.
- Changing oil hap-hazardly or not at all is, well, foolish to any sane person.
Why does lubricant exist? To serve itself and only operate in a vacuum of self-absorbed inner importance????? NO !!!!!!
Lubes exist to serve the equipment (engine, tranny, diff, gearbox, bearing, bushing, etc). Lubes have a purpose and that MAIN purpose is to reduce friction, which maximizes the equipment life by controlling wear. Should it matter if the lube in your engine was a 50/50 mix of goat milk and dog urine, if the outputs were excellent wear rates???? I'd dare say not.
Inputs are a great way to get drawn into a false sense of security, or an over-dramatized sense of panic. Unless there is a DIRECT CORRELATION of the input to an output, there's not too much to worry about. I am NOT saying inputs have no importance; that is patenently untrue. Inputs are excellent at predicting a potential for change in an output. If you see vis drop precipitously or FP go sky-high, you're going to want to watch the wear rates very closely, and probably at a closer sample interval. If you see K and Na jump up, you're gonna want to seek out a possible coolant leak, which could then turn the oil to gloppy muck and risk the loss of lubrication. It's important to watch inputs for sure, but it's NOT a cause just to see a change in an input and then automatically grab the wrenches. If an input changes a bit, look to see if the outputs are changing in an undesirable manner; if so, then change the oil. If not, then just continue to monitor wear rates.
Change oil when the wear rates become undesirable, typically in an upward trend which exceeds a condemnation limit. Otherwise, quit worrying about the inputs.
All the above being said, for "normal" OCI durations, it's become common place that TBN has shown no correlation whatsoever to wear rates in modern engines using modern fuels and modern lubes. Knowing the TBN/TAN is essentially moot in today's world because today's engines run clean enough that the properly formulated oils have enough base to deal with the expected OCIs. The rates of TBN degradation has not shown to be of risk today, so quit worrying about it.
I wonder if it was beginning to thicken up there towards the end. 
