I thought that even if the SysNAND was updated to a high version, it would still be possible to boot into an older EmuNAND without issues, since they are separate systems EmuNAND is on a partition of the microSD isolated from the SysNAND.
Activity
Pokemon Scarlata
all pokemon caught
Post in thread 'Pokemon Scarlet all caught pokemon save file'
https://gbatemp.net/threads/pokemon-scarlet-all-caught-pokemon-save-file.622240/post-10008439