We have seen threads like this in the past about different issues and their dating.
Here is one I started years ago and was met with similar pushback...
https://www.net54baseball.com/showthread.php?t=125883
I think this type of thread is what Phil was referring to with his post he made here.
At the end of the day with this set the most simple explanation is the best. It seems unless new information comes to light that there is NO indication that this is a multi-year issue. Why wouldn’t they have just all been made at the same time? Again, could it be a multi-year issue? Yes, but that is never the way you start dating a set, the most simple explanation is they made the set at one time, more evidence could change that but you need to prove a multi-year issue (not the other way around).
Based on that and the fact that some players are pictured in 1909 uniforms that seems like the most logical starting point. You can never date earlier because of potentially outdated information, but you CAN base a date off of when the earliest something could have happened... ie the first year a player was with a team, the appearance of a particular uniform being used no earlier than a known year.
In the case of NC Postcards Kevin makes a strong argument that the earliest this set could be is 1909, which may the right date. That being said the earliest postmark is 1910, which may be the right date. If you can find an indication of a much earlier PM on a card that could change everything bUt until then the cards should be dated “possibly 1909, but known to have been in distribution in 1910”