Mark,
Some of the variation is simply new graphic design.
I believe that the timeline went like this:
Blue & white boxes.
Blue & white boxes with yellow lettering.
Maroon boxes with gold lettering.
Black and gold boxes. I could be wrong, but I think these coincided with the introduction of scale cars. The scale cars have "O Scale Classics" and the non-scale cars typically say "Freight," for example.
Yellow and black boxes, which lasted up through K-Line's "acquisition" by Lionel. I've only seen O/O27 cars in the red and black boxes, and then later they introduced the "Train 19" blue and black boxes for O/O27 cars, but these were concurrent with the yellow and black boxes.
If you are looking for detailed scale cars, look for the black and gold boxes that say "O Scale Classics" or look for the yellow and black boxes that say "O Scale" in the upper-righthand corner of front of the box.
—Matt
