Good but not complete
Where is Peyton Randolph, the first elected President of the Continental Congress? Seven men served as President of Congress, well before George Washington was elected.
What about President John Hanson, the first president of the US under the Articles of Confederation? For complete accuracy there were seven other "Presidents" elected under the Articles, before the US adopted the current Constitution.
And there should be a footnote about the 1849 "president for a day" David Rice Atchison. Although the claim has been refuted, technically he could be considered to have been the acting President before Zachary Taylor was officially sworn in; a statue in his honor in Kansas City, MO says "President of the U.S. [for] one day".