Restore sav file from old sd card

Hey there,
I recently set up all my 3ds devices (don't ask please) with luma3ds cfw.
Most of them worked fine, but I had to reset a few of them in order to proceed.
The save files are all located in the old folder on the sd card as sav files, however the reset device fails to read them.
Is there any known way to get the contents of those save files now?
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Additional information:
The boot9.bin file I have is for the 3ds after the reset. I do not have one from before the reset because cfw wasn't installed back then.