how to filter dates from already present column?

how to filter dates from already present column(below program) with starting date as 19920102 and ending date as 20110930

Qtfdates = {};

for year =1980:2020

for month=3:3:12

Qtfdates{end+1}= datestr(nweekdate(3, 6, year, month));

end

end

vertcat(Qtfdates{:})