Evan, that's exactly what I did when I noticed the differences. The result was equal to the current one of CEC. When I decided to switch to Nextion and CEC, I first backed up the installed flash and eeprom, using AVRDUDESS. Those two files in HEX format, the 155KB flash and the 5KB eeprom, it was no longer possible to reload them on the NANO. Always an error message, I go from memory, by size. While a subsequent backup, when the problem already existed, was 78KB for the flash and 3KB for the eeprom. This last backup I could reload when I wanted. I'm not familiar with the Arduino language so I might have made some mistakes with AVRDUDESS on the first backup. I also tried reading them with NOTEPAD++, but they are just a sequence of hexadecimal characters.
73, de IK0XBC
IK0XBC