In column B, I am trying to add up the values in columns E, H, K, etc (every
third column), but ONLY if the corresponding date in columns C (for E), F
(for H), I (for K), etc (every third column) is within 6 months from TODAY.
I can move the data around if the values need to be next to the corresponding
dates, but that will move around some list validations I already have set up,
so I'm trying to avoid it if possible.

I think it is a sum if, but I can't get it to work. Any help is
appreciated. Thank you so much!