Not trying to be obstrepelous but if it's a question of only 1 cell  a month
what about setting things up for 12 months and writing stuff to the cells as
the data comes in.

I realy feel that if you could write a formula  rather than code for a
solution you'd be better off.

What about using COUNTIF?

I'm not a statistician really so I'm not sure how this would affect NVP but
the SUM formulas would be fine.

The problem with expanding the formuals with VBA is picking up the current
range to be expanded. Writing a formula to a cell is simple.
With string manipulation it wouldn't be too tricky tho as long as the target
cell is static so you could put a user function in there.
Are there any empty cells in the range to be SUMed NVPeed?