Bantam T3-C Shackle Change?

I have a theory that Bantam switched to a different style of rear shackles on the T3-C utility trailer. This is a collection of trailers that seem to all be sharing the same second style of rear shackles. By looking at the file name of each image you can see the serial number of the trailer. Serial Number 13661 is the earliest I have record of so far with an image, and 12956 has the ealier Willys Jeep style.