These surnames are connected by more than geographic proximity. While as yet can offer no more proof that basically what you have uncovered, I have become convinced that there is a certain connection. One of the telling points, how far back can you go?, is a hint at what point in time a surname came into use. Many of the possible spin-offs the Yearwood surname seem to have begun in the NC/SC areas. The Yearwood surname can certainly be found in early England. This may be true of some of the other names. This might be a point of research for someone with enough time to follow-up. I prefer the Yearwood surname as the root because I share it. Others might prefer another. Often, it seems in the records that individuals recording names found no distinction among the many spellings.