Create flag based on conditions

Hi all,
The scenario is when the user selects the start date and end date in the slicer, 
he will get the new opps in that period based on condition.
New opp means in the selected period the opportunity becomes open for the first time(means pipeline flag becomes Y from N).
and if it was Y before the selected period then it is not new opp
Opp Number is coming from opportunity table,
snapshot date is coming from snapshot date table,
Pipeline flag is coming from Pipeline flag table.
And none of the tables is directly connected to each other.

Start date and end date can be the external date table that we imported or calculated in the power bi or it may be snapshot date.
How can we do that?

Thanks in advance