Hello @JPickham ,
I like the idea shared by @karstenkoehler , And to adding my point for a report I suggest you to create a custom property and name it something like Lead date and you can create it as dropdown type and for each 9 list you can assign values to contacts like for Jan leads you can update this property for each contact inside Jan list with value of January similarly for rest and then at last when you create report you pullout this new property and I think it will create similar report like you shared screenshot.
Thank you
Shubham Nigam