In matches where Duckworth-Lewis revised targets are set due to interruptions which reduce the number of overs bowled, those revised targets and revised overs are used to calculate the net run rate for both teams.
For example, in a 50-over World Cup first-round group match, Team A are dismissed for 165 in 33.5 overs.
Team B progresses to 150-2, but play is halted after 26 overs due to rain. And the match never starts. The DL par score for team B is calculated as 149.
Because the target was revised, and Team A were bowled out, Team A's total is reset to 149 from 44 overs, thus their RR = 149/44 ,approx 3.39. Team B's RR, however, is computed as normal:150/26.33 ,approx 5.70.
Computing the match NRR for Team A gives us 3.39 - 5.70 = -2.31. Team B's NRR is: 5.70 - 3.39 = 2.31.