@herclau
Yes, that is it. All that it is doing is switching to an older notation for referencing cells; they are the same cells with the same formulas, though they will appear different. To work, the convention you use to reference a cell must be the one you have selected in options. If you change the option, Excel will change the manner in which it displays existing formulas.

__R1C1 Notation.__
R1C1 itself is an absolute reference to the cell in the 1st row and 1st column, that is $A$1.

With square brackets, the reference becomes relative, so R[-1]C[-1] is one column to the left and one row above the active cell. To describe this relationship using the A1 notation, one has to define both the active cell and the referenced cell. For example, a formula in cell C5 would show B4, in this case, and it continues down with C6 referencing B5

*etc*. The other slight catch is that R[0] and C[0] are abbreviated to R (the current row) and C (the current column) respectively. Using the A1 notation these would be 6:6, B:B

*etc*.

Working backwards from your name listing

**actualR...Datos!H15** implies the formula was written in cell

**I16**
whereas

**prior...…..Datos!H18** implies that formula is written in cell

**I19**
Whoever thought the A1 notation was simple

Do bear in mind

@vletm's point that you are pushing the limits of what might be reasonable to expect Excel to perform. It used to be the business data analysis community that pushed those limits but the 'slicing and dicing' of large datasets has now largely moved to Power Query and Power Pivot.