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If you look at the kingpin retaining pin, you realize that the body of the pin is "straight." If the kingpin isn't in place the retaining pin can slip right through the axle. (later pins without the "nut.")
It's the little "ramp" or wedge on the retaining pin which holds both kingpin and retainer in position. BUT - you have to have the nut on the correct side of the axle to get the angular orientation of the wedge correct to make the pins line up with the brake lever housing. Get the retaining pin backwards and the brake parts don't go together.
Thusly the axle has no "orientation." But the retaining pins do. (maybe not so for early axles but very much so for the early pins.)
And yes, to reinforce Tom's comment about the cones/tester. Almost ALL Model A front axles have some sort of "bend" to them. Usually winding around the spring perch/wishbone attachment with the wheel "rearward." Some of this, perhaps all, can be compensated in wheel alignment. Which is why there hasn't been much call for "testing."
Joe K