Pre-plastic is what I call the time when BRIO would hardly use any plastic in their railway products, except for the wheels of the trains and some minor bits here and there. That means almost every item before 1991. For me that represents a break in their history, a clean separation. 1991 is when they really started amping up the use of plastic in their line-up. All items that appeared before 1991 are tagged with "pre-plastic" even if they were sold after 1991. There are also a couple of items released in the early nineties, like 33594 Truck that still carry the same look & feel. Such items are included here as well.