I think my original question was too complex. Here's a boiled down version.

I want a formula in a cell to calculate a cell reference based on a number
in a different cell. For example:

- Cell B7 contains the value 90
- Cell D7 contains the formula: ='Cumulative data'D90
(Cumulative data is a sheet name)
- the row "90" called in the formula needs to be inserted by referring to
the value of cell B7.

Is there any way for me to do that?

Any help is appreciated,
Don