This is a little late, but I hope not too late. Until Feb. of 41, national insignia were on both wings, top and bottom. In that month, the insignia was ordered removed from the upper right and lower left wings. Then, in March of 42, they were replaced, so that there were four national insignia on the wings. In May of '42, the red circle was ordered removed from the center of the national insignia. For Operation Torch, in November of '42, all US aircraft were ordered to have a yellow surround put on the insignia on the lower wing surfaces, only. (This was out of concern for recognition by ground/surface forces.)
In May of '43, the insignia was ordered removed from the upper right and lower left wings again. In June of '43, the white bars were added, and the entire insignia was surrounded with a red band. In Sept. of '43, that red surround was changed to blue.
In practice, some aircraft were several months behind the curve on getting insignia changed. There is a picture of a Corsair squadron in the Solomons with three different variations of national insignia.
For reference, check out this site: http://www.history.navy.mil/faqs/faq2-1.htm