Every ten years. - 2017 US Mint 10 coins Proof Set, minted in San Francisco with COA and OGP. - 1977 US Mint 5 coins Proof Set, minted in San Francisco, with OGP. - 2007 US Mint 10 of 14 coins Proof Set, minted in San Francisco with COA (interesting toning on the one cent, see photo) and OPG.
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