Any copper coin that loses detail after soaking in peroxide, was not destroyed by the peroxide, it was destroyed by the corrosion that was holding the "details" you saw before cleaning. Peroxide removes dirt and grime, not solid metal, but when those who say they lost the date or details, well, that is becuase ther metal was severely corroded underneath (exfoliated corrosion) or just plain corroded. Dirt gets under it and air and when you soak it loosens the corroded, flaky metal and off it goes, especially if you rub the weak areas.
No cleaning will repair corrosion damage, not olive oil, mineral oil, peroxide, soda wash and aluminum foil and myrid of other ways to "clean" coppers. I have gotten many coppers over the years and continue to use peroxide on all, but will vary the time and amount of cleaning I will do, based on how bad the corrosion is. Sometimes I stop very early, satisfied that any further soaking will just make the coin "appear" to be worst. One reason I stress, always take a "before" photo of a copper before cleaning, so you can possibly get enough from that photo to ID, if after cleaning some details wash away.
Basically the coin is what the coin is when you find it, if not heavily corroded they should clean up beautifully, if not, blame the soil, not the cleaner.
