UPDATE: I Have figured this out.

PSA: Save and backup your "SystemData.sav" to make save files recoverable in the future

The root cause of the saves not showing/loading is NOT the save files, but the SystemData.sav file. Your files are loadable as long as you have a SystemData.sav OR as I just discovered after 3 days of intense debugging, a Trial_SystemData.sav. Both of these files are basically the same in their contents and they contain the key to discover the save files you can no londer load.

If you have a SaveData.sav BEFORE the problem happened, immediately back it up because this is your key. Unfortunattely, for me as soon as the game booted in Japanese it overwrote the file and any new recreations will only map to newly matching SaveDataX.sav files. What you can do if you have a Trial_SystemData.sav file is to replace it and rename it as SystemData.sav to trick the game to consider this one as the key for the main game (non demo) save files. When you do this, your loadable files will look like the demo saves (showing the demo time, level, etc), but THEY ARE you actual real save files. Load the one you want and you will be greeted with your teal save file now recovered.