Jim, While "The Address of the People of South Carolina, Assembled in Convention, to the People of the Slaveholding States of the United States." adopted on 24 Dec 1860 and published in the Charleston "Courier" on 25 Dec. of that year will not do as representing official direct contact between SC and the other six states, and the dates tell us it was not prior to SC's own secession; still, I felt it worthy of attention, given your question.

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Regards,
Penny