The U.S. Postal Service typically issues a stamp for former presidents on their first birthday after their death. That would put a stamp for the 39th President on or about October 1. It has not yet been confirmed by the USPS.
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President Carter was a US Navy Submariner ( LT ) Possible ceremonies at King’s Bay Naval Station, King’s Bay GA 31547 ( TRIDENT Training facility / Sub base ). FDoI Probably Plains GA or Wash DC.
I would suggest the Jimmy Carter Presidential Library & Museum in Atlanta, GA.
This would also make it easier to do combo covers with the Presidential Libraries stamp & the Carter stamp.