Interesting views - as I said I havent had any problems YET
probably wouldnt ever because not many people reprogram tens of thousands of times. typically a few dozen or hundred. and you might not notice that the 10-20 yr retention spec was compromised.
eeprom tolerates about an order of magnitude more cycles so unless writing constantly wouldnt notice there either. rare applications that reprogram flash a lot and need long data storage might have a problem though.
also worth noting that the programming timer is not influenced by clk prescale so while slowing the cpu helps with power consumption, it does not fix the flash retention problem.
I also tried using standard xtals, I bought a range to try, I could only get to 24mHz before it became hit and miss...
glad to see you were able to duplicate my own crystal experiments.
they are so cheap i also have dozens of different crystals, even hundreds for common values like 16mhz. not that unbelievable.