Corrupted NAND that I didn't know the backup was corrupt

[pcwizard7]

I have just spent the night trying to fix a switch that would go to black screen after Nintendo logo and long story short it was the restored NAND backup. Now luckily I keep previous backups of NAND for each fw update and restore previous one,

Then it crashed on first boot to home screen so i went into hos recovery mode and updated to current fw then went into it again and did factory reset for fresh start.
Then setup how i liked it and did a fresh backup

now that everything fine I like to know where it got corrupted as this first time its happened. only time i can think were it happened is when after NAND backup creation moving to the pc. but the sd car was fat32

thanks

 

[Draxzelex]

I mean it was either the transfer to or from the computer since Hekate verifies the backups it makes.