Tim's VCBC article mentioned is the best in depth study on T207's...I second Mike's recommendation.
Below is an overview of the set that Mike (above) posted here. There are also other great T207 threads on here as well...I will add some more links if/when I come across them.
https://www.net54baseball.com/showthread.php?t=221863
Here is the set checklist on the Old Cardboard site that identifies whether a card is from the Recruit/Napolean group or the Broadleaf/Cycle group. Pretty much any from the Broadleaf/Cycle group will be tough to come by, and there are definitely 40 to 50 of the Recruit/Napolean group tougher by various degrees (but in general not as tough to come by as the Broadleaf/Cycle cards):
https://www.oldcardboard.com/t/t207/t207list.asp
And here is a fun article from the Prewar cards site about collecting the set:
https://prewarcards.com/2021/08/03/a...ally-complete/
Brian