DaveO wrote:
LOL! Think about the capabilities though. I could be in an area,shoot wildlife with the D500 and then pop the same card into the D810 and shoot landscape in the same area. When you shoot four thousand or so pics on a trip,it would be nice to group them together geographically. I posed this query to Nikon support and should get a response in a few days,but I know we've got experts here on the forum who would be faster and reliable.
With those cameras it won't make any difference which camera formatted the card nor any difference which camera last wrote to the card.
To be honest though, I would put an XQD card in the D500 and a CF card in the D810.
Enjoy yourself.