The first Bicentennial coins to be produced that were intended for the public were dollars, struck during February 1975. The first for collectors were struck at San Francisco on April 23, 1975. The San Francisco Assay Office struck the 45,000,000 silver coins first, producing eleven million sets in uncirculated and four million in proof, then began the base metal pieces. Once striking began, the Mint found that the copper nickel dollar was striking indistinctly, a problem not seen with the silver pieces. The Mint modified the dies; the most noticeable change is that the revised issue, or Type II as it came to be known, have narrower, sharper lettering on the reverse. All silver pieces (struck only at San Francisco) are Type I; all three mints struck both Type I and Type II copper nickel pieces. All dollars included in 1975 proof sets are Type I; all those included in 1976 proof sets are Type II. Bicentennial coins for collectors were not delivered until after July 4, 1975. The Bicentennial pieces, in base metal, were included in 1975 proof sets and mint sets together with 1975-dated cents, nickels and dimes.