The stored checksum is updated with every write to memory. But, it doesn’t recalculate the entire checksum (too slow), it just updates if for the new data. This means that if it was bad before a write, it will still be bad (255 times in 256).

Thanks Nick.  After I replace the battery, I’ll try some experiments just as an exercise in curiosity.  For example, I’ll change the setup, save, and restart to see if the checksum error goes away.  If not, repeat for routings.  If not, finally repeat for presets.  At the end, if the error still occurs, then I’ll do a reinit.