Entering data in cell with formula breaks autofill of formula for new rows in table

In my table, column N in each row needs to be filled out with either 'Yes' or 'No'. Column O and column P both should have 'N/A' if column N is 'Yes', but if column N is 'No', Column O and P should be blank and have a date entered in it later.

This is accomplished by the formula =IF(N3="Yes"; "N/A";""). The only problem is that when I then enter a date in Column O and P, this breaks the autofill formula, so any new rows added don't get the formula =IF(N3="Yes"; "N/A";"").

What might be the best way to get around this?