Yes, that's why I said "This is assuming" in my post...
And that's why I started out by asking you why you needed so many, so I wouldn't have to assume any more...
OK, here's my method: When shooting around town, nearby, close to home, taking day trips hither and yon:
Shoot cards 1 & 2 in slots 1 & 2, with slot 2 as back-up. When they get full, set them aside and replace with cards 3 & 4. When then get full, set them aside and replace with cards 5 & 6. It would be
months before I need to return to cards 1 & 2. This gives me several months of temporary back-up, even though I have a rigorous ingestion and back-up routine in-place and have never needed to resort to going back through cards to recover an image.
However, this method
could fail when I take an extended trip away from home. So, my method on the road would be:
Put cards 1 & 2 into slots 1 & 2, and shoot slot 2 as back-up. At the end of the day, copy card 2 to an external hard drive. Put card 1 aside.
Reformat card 2 and put into slot 1. Insert card 3 into slot 2. At the end of the second day, copy card 3 to the external HD. Put card 2 aside.
Reformat card 3 and put into slot 1. Insert card 4 into slot 2. At the end of the second day, copy card 4 to the external HD. Put card 3 aside.
Reformat card 4 and put into slot 1. Insert card 5 into slot 2. At the end of the second day, copy card 5 to the external HD. Put card 4 aside.
Continue this routine until end of trip and I can copy all the images into my normal ingestion and back-up routine at home. This gives me all my images, in order by card number, from fresh, reformatted/unread cards, as well as an external drive with copies of everything. So I arrive home with at least two copies of everything, on two separate/independent media.
Then I would return to my 'normal' routine of card swapping.