In SC you can in fact slap your tag on there for 14 days before you ahve to register it.
"Up to two weeks", in my experience, usually means 4-6 weeks. Just FYI.
If you still have the PO's tag, you can run that. He still owns the car, after all. But don't put a tag from a different vehicle on it. That's a big no-no in NC.
Does SC still let you ride around with no tag at all? I used to see cars with no tag or a sign saying "Tag Applied For" in the back glass...
I transfered my insurance on my tag to my new car. Is that still a no-no to use the tag?
Then the dealership accidentally gave us somebody else's tag for the new car, and we drove around like that for a few months before anybody figured it out.