Data Validated Cells' Lists reduce but only in one column

Column O - master list of all names
Column N - an indexing formula that is watching C10:G38 for values that match the column O list, if no match, it puts a unique number in this column
Column P - the List2 that is created from ONLY the values in column O where there is a number in column N, so this list shrinks itself

List2 is then used as the DV source in the cells in C10:G38.



From this you can expand as you wish. If you were to add cells in column J for instance to also use List2, you would adjust the formula in column N to also include those cells.