If the "P_L Unrealised USD" for the next 3 Files equal the same value then mark all files following this as a duplicate.
In the attached App, bookmark SM2 example all files, any files beyond Futures Log_171213 with value Unit 1 = 1,486, Unit 2 = 1,253 should be marked as a duplicate but this will be decided after Futures Log_171215, ie. after the 3rd time it appears. !