I want to know the answer to the following question:
In what year was the local postage stamp overprinted and has since been replaced?
All the background I'm provided with is that "Because Guam is also part of the U.S. Postal System (postal abbreviation: GU, ZIP code range: 96910–96932), mail to Guam from the U.S. mainland is considered domestic and no additional charges are required.". Is that enough to answer the question?