If you are having soreness anywhere other than your sitbones, your saddle probably does not fit right. If your soreness is only on your sitbones, the saddle is working as intended.

Your sitbones area gets tougher and used to riding the more you ride. Based on the 900 miles you have done on that saddle, I wouldn't guess your sitbones would still be bothering you, so the problem is probably a bad saddle fit.