Unless one is using a color temperature meter and filters extremely well, changing filter packs can NOT be avoided. I beleive that the last 20 years has improved the batch to batch characteristices of color paper substantially and for the better. Unfortunately, there is not now and may never be any absolutes in the paper's manufacture. Even if there were no changes between batches that still would not negate storage and usage changes. Obviously the major lack of uniformity is in the scene itself and the handling of the photographic negative making...exposure, development, lighting conditions and the negative's manufacture.