Questions On WWII US Marine Letter

Appreciated thoughts on my assumptions regarding this cover:

I assume the December 25, 1944, postmark would have been applied at the point of origin. At the time, Marine Fighter Squadron 222 (VMF 222) was located on Nissan Island in the South Pacific.

From there, this letter would have traveled to the Fleet Post Office (FPO) in San Francisco before being dispatched to Cudahy, WI. My hunch is that the stamp on the back is a receiving mark applied at the Geo. J. Meyer Manufacturing Company in Cudahy, not at the FPO. My reason is that I can find no evidence of this type of mark being used at the FPO.

Thanks!