Hi,
If your eeprom data is corrupt you should be able to rewite it to the same locations.
If the locations are damaged then you may be able to use other locations.; depending on how bad the damage is.
In general use I think its very reliable.
Some time ago I did a read / write test on the eeprom of a 16F876A to prove it would be reliable for my project - I repeatedly wrote to then verified of the whole eeprom area, took a couple of weeks to do that, it was only after 500,000 write that I had one byte fail.
The byte of memory was defective, not just corrupt, but all other locations were still usable.
In practice it mean my project could backup key paramenters for 10 years with little chance of failure, which is probably more than the expected life of the whole pic chip.