DAX

Anonymous , Try

Last Date = CALCULATE ( MAx ( territory [Date] ), ALLEXCEPT ( territory , territory [policy number] ) )

second max date  = 
VAR __LAST = [First Purchase] 
RETURN CALCULATE ( MIN ( territory[Date] ), ALLEXCEPT ( territory , territory [policy number] ), Dates[Date] < __LAST )

Or have Rank and filter for 2

For Rank Refer these links
https://radacad.com/how-to-use-rankx-in-dax-part-2-of-3-calculated-measures
https://radacad.com/how-to-use-rankx-in-dax-part-1-of-3-calculated-columns
https://radacad.com/how-to-use-rankx-in-dax-part-3-of-3-the-finale
https://community.powerbi.com/t5/Community-Blog/Dynamic-TopN-made-easy-with-What-If-Parameter/ba-p/367415