Concatenate Sum Range & MAX Formula

I have a column at the end of the table that sums a number of months.
What I would like to do is have the formula adjust based on a seperate formula.

Below might illustrate better than I am explaining:

Current formula:

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What I would like to do is make the "MARCH" piece dynamic based on a MAX date in a seperate table:

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Here is what I have tried.

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Where the cell "CB37" had the MAX formula listed above

How can I concatenate the MAX formula, or the cell reference to accomplish this?

That is sort of where I was heading:

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I was trying to build the actual formula into the SUM, is that not a viable option?

I am however getting a #REF! error with:

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Here is what I have,
I had to remove a good deal of info, so the problem is the same, but the cell reference has changed

This is GREAT!!

I didn't think of this before, but can it reference a named range?

So instead of "CB$37" its something like "SUM_THROUGH"?

My thought is that I have other tables I going to use this formula on, and I'd like to have a cleaner way to refer to it?

Sorry,
It was as easy as:

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Thank you again for your help!!