I think there's a fair amount of evidence that a gradual transition had begun prior to 1900. Walt Snyder's Ithaca book, p. 243, shows photos of Ithaca catalogs from 1886, 1892, and 1900. All three guns featured on the covers have PG's: semi or round knob on the first two, squared-off PG on the 1900 book. Photos of the Crass model seem to show the same progression: round knob on the early guns, full PG on the later ones. Brophy's L.C. Smith book also shows quite a few photos (and catalog pages) of pre-1900 guns featuring PG's. Again, many of them of the round knob/semi variety.
