New Fields on -Assign Vendor on Exception Threshold Setup

Hi

While assigning vendor to Exceptional Threshold setup there are new fields in 12.2.5

1. Prospective Check Box

2. Start and End date of Certificate.

What is the role of these two fields ?

How can we achieve if supplier provide certificate to deduct lower rate TDS for cumulative invoice amount say 100000/-

And any amount after that should be deducted on regular rate; when I am defining this and if I enter first invoice say 105000/- TDS is deducting @ higher rate on total amount of Invoice. Though expectation is that lower rate should be on 100000/- amount and higher rate on 5000/- amount.

Thanks