So yesterday the grand total was somewhere else, like column J but today it is in column K? I think fixing that would be the way to go. How does the data get there in the first place? If that can't be fixed, I can only imagine that your formula would need to use a function that returned the grand total, but how to find it? Perhaps based on a column header text? A cell with the words "Grand Total" beside/above the total?
While I marvel at the Excel formulas that people come up with, they are not my forte so you might wait for a formula suggestion.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.