Possibly the only times I've ever seen CRCs expose bad data in my EEPROM, was due to the power going out during a write. The data changing on its own really isn't something you should see for the 10 year retention period, and I've yet to perform a test that long. If you write to the EEPROM regularly, however, you are always going to have some time when you lose power in the middle of a write.You are mostly protected with redundant copies, however. If the power goes out while writing the 2nd copy, you still successfully wrote the 1st copy which can be validated with its CRC. If the power goes out while writing the 1st copy, the 2nd copy still contains the data from the last time it was written.Getting back the data from the last time you wrote isn't perfect, but at least you don't lose everything and it's the best you can do without adding some kind of capacitor backup.When I made the code in this thread that burnt out a memory location, I actually did rerun it a few times. Interestingly, the burnt-out memory location did pass another ~10k write/read cycles before it failed again. Even after running the sketch several times, the burnt-out location would write/read a few times before failing again.