In an ideal situation, the catalog sort value for variations of the same product would have the same sort value. If you for some reason can't assign the same value for all the variations, the sort numbers have to be consecutive. For example variations of the same product, A, B, C, D, and E could have sort values 1, 1, 1, 1, 1 or 1, 2, 3, 4, 5, but not 1, 2, 8, 10, 11.