This is a thought that bugs me long time now.
My oldest bike with more than 80.000 km's had never checked the valve clearances.
At 78000 km's I checked the inlet valves to find them almost having zero clearance.
This to me means that the last 50.000 km's most probably the bike was having tight inlet valves but with no loss of compression or burnt valves.
Why is the question...
maybe the valves "ate" their seats and then the 0.15mm gap was not translated to lost compression because carbon rersidue on the valve stem and seat filled the void...
...and maybe this led to a partial cooling of the valve that along with the air/fuel "shower" prevented them from burning...
What do you think? (i.e. an can of worms due to open!)
you seem to have an intuitive feel for things mechanical!
all I can add is that a well run-in engine has a good start in life and if it is then well maintained with good quality oil, wearing surfaces seem to settle down, with low wear after that. this seems to be the case with your engine
crankshafts commonly show no measureable wear even after half a million kms.
at the other end of the scale, totally worn out pistons and rings will "build" carbon deposits in just the right places to maintain compression and prevent piston slap. the big American V8's are known to tolerate the most incredible abuse without breakdown.
Wow what a compliment!... Feeling humble already...
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