That's an interesting question.
Let's start with the timeline of these AB 350, BROAD LEAF 350, CYCLE 350, and DRUM cards. American Litho started printing these backs in the Summer of 1910.
Perhaps, the DRUM's may have also continued into the Fall of 1910.
The timeline for the AB 350 (no frame) cards is circa Fall/Winter 1910. Finally, the AB 460, LENOX, and UZIT cards in the final T206 print runs..circa Feb 1911.
Note that all 4 of these backs are without frames.
Now, the timeline for the PIEDMONT 460, Factory 42 cards is somewhat uncertain. I think it possibly was in late 1910, since all 63 subjects in the 350/460 series
were printed. But, only a dozen (or so) 460-only subjects were printed with PIEDMONT 460, Factory 42 backs.
TED Z
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