It is true that some drivers need to be rotated 180 degrees due to becoming off centered. It has to do with the weight of the driver putting pressure on the surround over a long period of time. This is less likely to happen with smaller lighter drivers than with larger heavier drivers and the surround material has a lot to do with it. For example, a 12" poly cone woofer with an inverted butal surround would most likely benefit from periodic rotation.
If your drivers need to be rotated you should be able to see a difference in the width of the surround by comparing the top to the bottom.
If your drivers need to be rotated you should be able to see a difference in the width of the surround by comparing the top to the bottom.