Valve seat recession was real and identified in extensive laboratory testing
OF AIR CRAFT ENGINES when running in lean burn conditions as is done at high altitude.
It was never ever found to be a problem in auto engines at sea level.
But the technically illiterate who write 99% of all motoring magazines got hold of it and ran hard.
Did wonders for sales as owners desperately needed to know if their precious possesions were going to self destruct.
Naturally the snake oil salesmen followed hard in the footsteps .
For carburettor engines there never was a problem.
Some blown engines could be adversely affected.
I used to do thousands of miles on my M20 and the only valve problems has been a single burnt exhaust valve.
Done enough miles to do a full series of rebores on one barrel out to +80 and no vlave problems.
The people who had problems were the clots running 11:1 to 12:1 which is right on the limits so they either had to detune or run