Jazzbaby first appeared in Romeyn Falls (now Astro City) just as jazz music took form and became a prominent part of American popular culture. The precise date of her debut is unknown, but can reasonably be estimated as sometime between America's entry into World War I (1917), and a known interaction with Dame Progress in 1919.
If the Broken Man's tale is to be trusted, she is a later incarnation of Mister Cakewalk. This would suggest that she is also connected with The Bouncing Beatnik and The Halcyon Hippie, and that the association between the four characters is somehow based on the music of the times.
There is also a suggested hint that the destruction of Silverstring's guitar in the late 1800s, was the catalyst-force behind the sub-culture personas defining this entity or entities as it travels through time.