If(Date#(Year&Month,'YYYYMMM')>=Date#('Oct'&(Year(Today())-1), 'MMMYYYY') and
Date#(Year&Month,'YYYYMMM')>=Date#('Mar'&(Year(Today())), 'MMMYYYY') , 1,0) as Flag
From <>;
This is just an idea. You can make it more dynamic and might have to adjust it accordingly. Hope this helps. Or the same can by done using a preceding load with less complex expression.