Question NOR flash memory

I don't want to lose retention
manufacturers of NOR flash memory chips say that they retain data for up to 20 years but I am doubtful if it is possible to increase this retention estimate a lot? I write the firmware only once in the flash memory and store it

Have a read of this document, it appears that the number of write erase cycles and temperature are the two important factors. Figure 3 suggests yours should last ~100,000 years!!!

Mike.

the firmware was recorded in the NOR flash memory only once, regardless of what I do, will the data be erased?