We know 12-bar and 16-bar blues were both known at all in the New Orleans area by 1908, because of e.g. the blues Antonio Maggio and Emmet Kennedy heard and were inspired by. The live issue is, how much did the likes of Bechet and Ory generally care about blues music before about 1912? Because the blues that jazz musicians ever recorded, no matter their age or when or for whom, tended to sound a lot like what was published as blues sheet music during 1912 on, rather than e.g. the normal 16-bar folk blues that were known to the likes of Mance Lipscomb as of about 1911.

(Emmet Kennedy's and Roy Carew's recollections are valuable. They were both interested in black folk music generally when Son House was two years old, and they compared notes with each other.)