Well, this is speculation on my part in this instance, but in my previous experience with fiberglass work, I have learned that after several uses, the molds/dies need adjustment, and occasionally, you will find slight variations in the materials.
The machines are then re-adjusted or re-aligned, and molds are re-lined.
Some of the last runs right before the resetting are sometimes sold at a discount, as they take a little more work and effort to install, without effecting the quality.
My previous experiance was with Jeep and Landcruiser bodies, so I by no means am an expert, just thinking that the same logic applies here.
