Richard – Again thanks for your question and I will answer it as best I can. Feel free to ask me to clarify anything.
Your question was “How do I know that the 150-350 Southern Association subjects were not printed simultaneously as the 350 Only subjects in the T206 set?”
I will start broad and work my way to the more detailed parts of the explanation.
The T206 set was printed in three different series 150, 350, and 460. However the subjects groups were not just printed in each of these series. Some carried over from one series to the next. Years of collectors and researches compiling data on the possible front/back combinations of each image has made it possible for us to group the subjects. Traditionally we use the terms:
150 Only
150-350
350 Only
350-460
460 Only
These groups have clear delineative patterns that have lead to this terminology. It’s these patterns that show us the groups where printed for a period of time and then discontinued to make room for the next group of subjects. If this was not the case then we would have random subjects showing up aross the different series or even the entire printing of the set. Once a group was removed and the next group began being printed the discontinued images were not printed again. For example we don’t see any 150-350 series images brought back for a print run during the 350 Only, 350-460, or 460 Only groups.
Now that we have established that the groups were printed separately let’s explain the common backs like Piedmont 350 in which you can find multiple groups. Many collectors have the misconception that when the Piedmont 350, one of the other common backs, or an Assorted back were printed in the “350 Series” that all of the images were printed in one big group. Keep in mind that this was an ongoing project that lasted for 3 years and the flag ship back brands were printed over and over again. When the 150-350 series transitioned into the “350 Series” ad back printing they were printed with Piedmont 350 backs. When the next print run began of 350 Only subjects they were printed with Piedmont 350 ad backs. When the 350-460 subjects were introduced they were printed with Piedmont 350 ad backs. This results in a large group of Piedmont 350 subjects but they were not all printed at the same time but rather in small groups over a long period of time.
A great example of how subjects from different groups could receive the same ad back but were printed during different print runs, are the Sovereign 350 back group. When the 350 Only subjects were discontinued and the 350-460 group began printing ALC changed the color ink. It was a subtle difference but draws a very clear line between the two print runs. You will not find a 350 Only subject with an apple green Sovereign back and you will not find a 350-460 subject with a forest green Sovereign back. Two distinct print runs that if it weren't for the color change in ink could be thought to have been printed at the same time.
The assorted back brands were printed in the same manner. During a print run of 150-350 some of the cards would receive an assorted back ad. During the 350 Only run a group would receive the same back ad. At the end of the entire T206 run there would be a large number of subjects printed with a particular ad back but they were printed during their respective groups print run.
Now let’s talk about the 48 southern league subjects and specifically the 20 Southern Association players. Originally all 48 of the southern league players were intended to be printed in the 150 series Brown Hindu group. That number was reduced to 34 and the other 12 were not printed for the first time until the “350 Series” began.
For more on that you can read this thread.
http://www.net54baseball.com/showthread.php?t=125317
When the “350 Series” began printing the first print run was comprised of subjects from the 150-350 group and the additional 12 southern league subjects. Take a look at the back of Leon’s card.
This looks like a mess to a lot of people but to me it’s a beautiful snapshot of the time the 150 Series was transitioning to the 350 Series. The first subjects printed in the 350 Series were printed with Piedmont 350, Old Mill, and EPDG backs. You will see all three back ads printed on Leon’s card. Two groups of cards show this to be true.
The Southern League players were printed with the Piedmont 350 and Old Mill backs. Once this run was complete they were not printed again. The next group included the 9 350 short run players. Linadaman, Dahlen (Boston), Karger, Mullin (horizontal), etc. These players were included in this initial run and printed with Piedmont 350 and EPDG backs. You will not find any of these subjects with other ad backs that 150-350 subjects can be found with such as Sovereign 350 or Sweet Caporal 350 Factory 25 or 30.
All of the above is why I believe that the Southern Association players were never printed on the same sheet as the 350 Only subjects during the T206 set.
Am I right? You can decide for yourself. I highly recommend anyone that cares to look this deeply into the composition of this set and other relating sets to do their own research. There is a lot of bad information out there coming from well respected sources. Do I know everything about the set? Absolutely not and I am going to make mistakes or be proven wrong about something I post. When that happens there will be at least one and probably few that will relish in their Aha!! moment. That's fine with me as I just really care about knowing what's right more than being right. That means that if you have any insight into this set you can contact me via the board, email, or PM and I will gladly listen whether you're a 20 year veteran of the hobby or just starting out. Nobody can figure this out on their own.
All the best.