All this talk about air drying for years is missing an important point. Holly is not like other woods. To avoid staining and keep its unique light color, holly must be dried very quickly. Again, I don't have personal experience with it, but the recommendations are not only to kiln dry, but to use a vacuum kiln, which sucks the moisture out more quickly than a regular kiln. In addition, they say that the tree should be cut only in the winter and the boards should be in the kiln within days. It may already be too late for this.
Cheers,
Keith