Dear Anshika,
Unique Visitors are sensitive to the granularity they are attributed in.
If you select 'Unique Visitors' break down by Day, Week, Month and Year, it will be equal to 'Daily Unique Visitors', 'Weekly Unique Visitors', 'Monthly Unique Visitors' and 'Yearly Unique Visitors' respectively but the total will be based on the time period you have selected.
Lets say, I have visited your page every day in 2017. This is how the report looks like:
Unique Visitor Report break down by Day(Entire Year 2017) - 365 count (Equal to Daily Unique Visitor) and total = 1.
Unique Visitor Report break down by Month(Entire Year) - 12 count (Equal to Monthly Unique Visitor) and total = 1.
So, as you predicted, the 'total' deduplicate the data for the selected period.
Thank You!
Arun