Accurate barrel life represents a shift point, where consistent best accuracy leaves.
To detect it, you first have to attain it.
If content with 3" groups then you're probably not going to 'see' further degradation anywhere near the accurate barrel life point.
Could probably shoot 5,000 28nosler rounds before it get's worse than 3" (when bullets start blowing up).
Another thing to keep in mind is that shot timing is a big influence to barrel life. You could destroy a 28Nosler barrel in one range session. My calcs for 28Nos default at 50sec shot rate, and 717 ABL drops to 144 ABL if you did a lot of group shooting with a 10sec shot rate. If you shot 1 every 10min you could probably extend ABL x2, but I have no way to predict that.
Pressure plays a big role, and of course powder temperature and amount.
If you wanted to manage it, moly (in particular) extends ABL by cooling the charge temp as it vaporizes. That's why you see MV drop with use of moly (not reduced friction). But then many people step up their charge to compensate, and barrel life goes right back down. So I no longer compensate for moly, and really it's surprising to me that anyone still uses it.