Johnson vs Demspey? Almost! Some say the fight happened in Canada, though there is only one report, which could very well be a fake.
Here's the lead up to the match that might have been, which Dempsey was reported to win via TKO.
More info. Another read:
JACK JOHNSON HERE, LOOKING HIS BEST; Ex-Champion Thinks He "Could Lick Dempsey"--To Spend Ten Days in Harlem.
July 23, 1921, Saturday
He admits that he is trying to come back, but to look at Jack Johnson you never could tell that he had passed his heyday. The big negro ex-champion arrived in New York yesterday aboard the Twentieth Century Limited from Chicago, looking more like 25 than the 40-odd years he acknowledges.