Clayton - The 48 southern league subjects were all printed with an Old Mill back that was used only for these subjects. The ledger page below shows the dates ALC began packing the Old Mill cards and shipping them to the factory. These dates are in the late summer of 1909. Also there is a hand written not that says: "Southern Leagues discontinued later part 1909." I think this unique back is fairly solid evidence of all 48 cards being printed at the same time during the PG1 production.
Group 1 subjects began being printed with Piedmont 350 backs in 1909. So it seems logical to me that all 48 SL subjects, who were in production at the time, were being printed with Piedmont 350 as well. In order for the 14 to be printed with PG2 subjects, ATC would have had to shelve them from late 1909 until several months into 1910, and then print just the 14 as was proposed.
