Nope. Although every code is unique, they can be shot in any order.
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As long as that customer's card(s) are re-photographed again prior to any subsequent photos of the subject, Snapizzi will assign them all to the same gallery for that customer. There is no limit to the number of times a customer can use the same camera card. They can always use a new card for other photo sets, but the result is they would have a gallery created for the number of cards they used during the event. Of course it is easier for them if they just use the same one.