Importance of consistency
A product line is, in most cases, a group of products packed in different types and materials of packaging. Each material is defined by its own limitations when it comes to color values and tonal range of reproduction. To make things worse, many of printed items are being printed on different machines. And machines are also defined by their own limitations. Double trouble. So, having that in mind, no wonder final products are far from standardisation and that's exactly what a product line should aim to.