The formula you are asking for will only work for the current week and not
previous weeks. You are adding either a row or column every week so the
formula has to adjust to the week number
you can use
=if(countif(A5:A20,A20)>1,true,false))
A20 is the latest pick and A5:A20 the range of all the picks
to make it adjustable
=if(countif(A5:A20,indirect(address(B2+4,1))>1,true,false))
where B2 is the week number. Because the range starts at A5, you have to
add four to the week number to get the row number.
