Quote: " It's an easy leap to say that if an oil starts out near 21.89 when new, then after a normal use cycle in the engine, it stands a better of chance of still being within the range and rated as a 50w oil, giving you the protection you need. " That statement is an assumption not a fact.
I don't think it is that easy to draw this conclusion from any of the oil tests that where done. One might think that is what happens but without actual used oil analyses it is not factual to draw this conclusion. For example there are many used oil samples that show MOB 1 Vtwin actually increased its viscosity.
Yes, it is an assumption but it seems logical to me. If you have plenty of viscosity improvers in the oil and they get damaged over time, then more VIs gives you more time. Possibly the quality of the VIs has something to do with it. But all things being equal in a specific engine, more VIs seems to equate to an oil that maintains its weight grade rating over time. IMO from what I've read.
True, used analysis would be the only way to determine how this aspect might actually play out. Probably quite difficult for the average person to hold all the variables to the same in order to assess multiple oils...only engines in a test stand at some test lab is the way to do this. There are ASTM tests that could do this - I'm aware of the Wear Protection test, the Oxidation Stability test, Volatility (or evaporation) test, maybe others that can give a better indication of long term performance of an oil.
I don't see how it is possible for an oil to INCREASE in viscosity over time...seems to me it can only degrade or stay the same, not get better. If an oil company can do that, they should be advertising that 'till the cows come up!!