Based on analysis of stud patterns and bottom texture, all samples share identical patterns on both upper and lower side of the bricks. Even if there are several different variations - even registered as different molds, it's clear evidence that only a single mold was used, and that it only contained one mold member. As the difference between the two molds is of a certain significance, they were registered as a separate evolution step, instead of just several more variants of the same mold.