It's been awhile since I posted Part I, so this follow-up is long overdue!I've put together another list of "firsts" within the US commemorative coin series and offer them here for a quick perusal. No "previously unknown" items here, just the result of taking a closer look at the coins. Enjoy!
Design Element FirstsPeople
First coin to feature a foreign monarch: 1893 World's Columbian Exposition Isabella Quarter Dollar - Queen Isabella of Spain

First coin to feature the same person on both of its sides: 1900 Lafayette Memorial Dollar - General Lafayette

First double-headed coin (i.e., a coin with a bust portrait on each side): 1904 Lewis and Clark Expedition Gold Dollar - Portrait of Meriwhether Lewis on obverse, portrait of William Clark on reverse

First coin to include a living person in its design: 1921 Alabama Statehood Centennial (Governor Thomas E. Kilby)

First coin to include a living US President: 1926 American Independence Sesquicentennial (President Calvin Coolidge)

First coin to depict an actual person vs. allegorical figure: 1892 World's Columbian Exposition Half Dollar - Christopher Columbus
This "First" applies to US coinage in general, not just US commemorative coins.
One caveat: No known portrait of Columbus was available as reference, so the portrait on the coin is an artist's vision of what Columbus might have looked like (based on contemporary descriptions).
Animals
First coin to include an animal in its design: 1900 Lafayette Memorial Dollar - Horse

First coin to include an eagle (the most commonly featured animal in the series) in its design: Tie - 1915 Panama-Pacific International Exposition, Half Dollar and Quarter Eagle

First coin to include a bird (other than an eagle) in its design: 1915 Panama-Pacific International Exposition, $50 Gold - Owl

First coin to include a fish in its design: 1934 Maryland Tercentenary - No species identified; meant to be representative of "fish" in general

First coin with a specific, named animal depicted: 2008 Bald Eagle Half Dollar,
ChallengerDates and Inscriptions
First coin to be dual-dated: 1903 Louisiana Purchase Exposition Gold Dollars (Jefferson, McKinley) - 1803-1903
First dual-dated silver coin: Tie, 1920 Maine Statehood Centennial and 1920 Pilgrim Landing Tercentenary Half Dollars

First coin to include: "Liberty" "In God We Trust" AND "E Pluribus Unum": 1918 Illinois Statehood Centennial

First to include a specific calendar date: 1927 Battle of Bennington / Vermont Sesquicentennial (August 16, 1777)

First coin to include commemorative dates plus the year of striking: 1921 Pilgrim Tercentenary - "1620 - 1920" plus "1921"
The 1921 Alabama Statehood Centennial soon followed, with 1921 on the obverse and 1819-1919 on the reverse.
Legal / Administrative Firsts
First commemorative coin proposal to receive Presidential veto: 1930 Gadsden Purchase 75th Anniversary

First commemorative coin to be struck for a US Territory: 1928 Hawaiian (European) Discovery Sesquicentennial
Hawaii did not become a state until 1959; it officially became a US Territory in 1900.

First Half Dollar with an issue price of more than $1.00: 1928 Hawaiian ($2.00)
Miscellaneous Firsts
First multi-year coin program: World's Columbian Exposition Half Dollar, Same design for 1892 and 1893

First coin to use an allegorical design: 1893 World's Columbian Exposition Isabella Quarter Dollar - Female figure representing "Women's Industry" (reverse)

First issue with non-date types or varieties: 1903 Louisiana Purchase Exposition Gold Dollars (Jefferson portrait, McKinley portrait)
First silver coins with non-date varieties: Tie, the 1921 Alabama Statehood (Plain and 2x2), the 1921 Missouri Statehood (Plain and 2*4)

First coin to feature a State Seal: 1918 Illinois Statehood Centennial (reverse)

First coin to feature a US Foreign Policy design theme: 1923 Monroe Doctrine Centennial

First coin designed by a woman:
Classic Era: 1921 Alabama Statehood Centennial half dollar -
Laura Gardin Fraser (This "First" applies to US coinage in general, not just US commemorative coins.)
Modern Era: 1982 George Washington 250th Anniversary half dollar - Elizabeth Jones

First multi-coin program to feature the same design across coins of multiple denominations: 1994 World Cup Soccer Coin Program. The 1994 World Cup logo was adapted by freelance artist Dean McMullen and was used as the reverse design for the CuNi Clad Half Dollar, Silver Dollar and Gold Half Eagle - the three coins of the program.

First multi-coin program to feature the same obverse AND reverse designs across coins of multiple denominations: 2014 National Baseball Hall of Fame coins. A depiction of a baseball glove was on the obverse and a baseball on the reverse of the CuNi Clad Half Dollar, Silver Dollar and Gold Half Eagle - the three coins of the program.

First curved/domed coin: Coins of the 2014 National Baseball Hall of Fame 75th Anniversary

First colorized coin: 2020 National Basketball Hall of Fame, Tie: CuNi Clad Half Dollar and Silver Dollar
If you'd like to review the Part I "Firsts", check out:
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Commemorative Firsts - Part I