Different "Nintendo 3DS" subfolder names = different movable.sed = different SD file encryption key, you will need the old one to extract your old .savs (from a nand backup, or maybe by bruteforcing a pre-6.0 game - if that's even possible with digital versions)
Hmm that might sound like a problem.
Maybe I have a very old nand backup somewhere but I will have to search different drives.
Pff why do they make it all so difficult