When I flew South African I credited the miles to DL. I was fortunate that there was a double miles promotion going on and I got double credits. The only thing was that my flights were actually ticketed by DL via a codeshare and one of the connecting flights was on DL (JFK-ATL) and the rest were on SAA. I do not know if the codeshare is necessary to get DL credits, but if you went to South Africa, you most certainly have a lot of miles from that trip and it would be a shame to lose them.