Need help changing my formula to retain cell/range references when sorting

I have read a couple of different threads where people have explained why a formula loses a cell/range reference (#REF!) when a column is sorted, and suggestions to fix. However, I don't know Numbers that well to use the function suggestions for my particular need and was hoping someone could help.

In my actual database, I have about 15 columns per row, including a first and last name column, a "checkbox" column (corresponding to each name), and a (hidden) column that counts (in successive order) how many "names" are checked off. This last column is used in another sheet for a Lookup function - to just list the names who have checkmarks next to their names. Out of about 50 names, about 10 are checked so I really don't want to duplicate the entire database and use "filtering".

See screenshot below for the current formula. It is the "orange" reference (D$1:D2) that loses its reference when any of the columns are sorted (in the screenshot below, last name is sorted).

Is there a different formula I can use that won't be affected by "sorting" using my current setup?

Thanks in advance.