I think with canon cameras they are always individual, but they might reset on firmware updates or something. I know that every time I format my memory card I don't get duplicate file names. The camera probably manages that that and counts how many videos/images its recorded over all the memory cards.
"you know when you see a edit with there colors boosted and they really hd?" -coleaddison
"When there are more people in your organization who believe Obama is a Muslim than believe in the theory of evolution, there is a problem." -colbert