I might be wrong but I didn't think there was a general requirement for bible students to preach back in 1919. Back then it was the colporteurs who did the work. Let the figures speak for themselves (sourced from A People For His Name, by Tony Wills)
Year/Peak Number of Colporteurs:
1914: "fewer"
1915: "fewer"
1916: 372
1917: 461
1918: 225
1919: 507
1920: 350
Contrary to Rutherford's later claims of there being a "practical silence" or that the work had "practically stopped" in 1918/19, the WT at the time acknowledged the war had "curtailed" the work but said "we are neither dismayed nor discouraged" (WT 12/15/18)