The default behavior for handling cards containing images is a read-only mount, and copy all the images without any modifications.
When flash fails it returns garbage or zeros instead of (what was) your data. It can be tranient or persistent. And without any error codes from the storage device or the file system.
If storage returns garbage for filesystem metadata, all bets are off how the OS filesystem driver will behave.
Reformat should be done in camera. And that card used only in that camera. And only that camera gets to write to that card. And don't delete individual images.