Before the axles were closed, another base modification was made. The supports were widened to 1.5mm and length was increased to 9.5mm. The open rectangles were made larger as well. So the base (or body casting which includes the base) had a total of four modifications (not the three that are commonly cataloged).
I suspect most people simply over look the two different open axle bases. The second modification may or may not be hard to find as there has never been much discussion about it. I suspect the second modification to the 1.5mm wide supports was short lived before the axles were closed.
