I think I get this. Here's an example
1st sitting
Unit 1 pass
Unit 2 pass
Unit 3 Fail
2nd Sitting
Unit 4 Pass
Unit 5 Pass
Unit 6 Pass
3rd Sitting
Unit 7 Pass
Unit 8 Pass
Unit 9 Fail
4th Sitting
Retake Unit 3 Pass
Retake Unit 9 Pass
Final result is a pass - and all sittings (up to six of them allowed), should be done within 10 days according to UK CAA rules.