6 retired on that lap, not 7. And I've not checked whether all 6 retired at the same moment and by the same cause. Considering 17 took the green flag, that's only about 1/3rd of all drivers... I don't see a reason for a rerun. Also, what has the Monza race to do with race 1 and why should it be voided?
Not sure where you got your numbers H. 15 drivers started at Goodwood. Nigel retired at 07:50 after his engine blew. Vos retired at 10:47 on lap 7 after he blew his top
leaving thirteen runners. Seven of the remaining runners then disconnected simultaneously at around 12:02. That left 6 runners. That means that more then 50% of the remaining field were involuntarily disconnected.
The options open under the rules were to take the result at the point of disconnect or Red Flag the event. Since Monza was not the reverse Spec race (for obvious reasons) I fully support Billy's decision to hold a new event. If you are cross at losing the win, I'm spitting feathers at losing my best ever finish. I also wasted two hours fully modding the event!
GPL Replay Analyser export - shows both the number of starters and the retirements lap by lap. 6 retired in a single lap.
Lap 8:
Paul Whitfield 65 overtakes Billy Nobrakes.
Paul Whitfield 65 overtakes Axel Cookie.
Paul Whitfield 65 overtakes Fulvio Policardi_65.
Paul Whitfield 65 overtakes Steve Bird65.
Paul Whitfield 65 overtakes Jason Blito.
Paul Whitfield 65 overtakes Göran Jonsson65.
Paul Whitfield 65 is in position 6 at the end of the lap.
Geoff Heard65 overtakes Billy Nobrakes.
Geoff Heard65 overtakes Axel Cookie.
Geoff Heard65 overtakes Fulvio Policardi_65.
Geoff Heard65 overtakes Steve Bird65.
Geoff Heard65 overtakes Jason Blito.
Geoff Heard65 overtakes Göran Jonsson65.
Geoff Heard65 is in position 5 at the end of the lap.
Ronnie Peterson overtakes Göran Jonsson65.
Ronnie Peterson is in position 4 at the end of the lap.
Göran Jonsson65 retires the BrabhamBT7.
Billy Nobrakes retires the BrabhamBT7.
Steve Bird65 retires the Honda.
Jason Blito retires the Honda.
Axel Cookie retires the BrabhamBT7.
Fulvio Policardi_65 retires the BrabhamBT7.and
RACE RESULTS (After 13 laps)
Pos No Driver Team Nat Laps Race Time Diff
1 12 Hristo Itchov65 Brab BT7 JPN 13 17m49.934s
2 1 65 evilclive Brab BT7 GBR 13 17m57.673s 07.739s
3 10 Sam Blood Brab BT7 GBR 13 18m24.759s 34.825s
4 15 Ronnie Peterson Brab BT7 ITA 13 18m29.586s 39.652s
5 18 Paul Whitfield 65 Honda GBR 12 18m09.175s 1 lap(s)
6 17 Geoff Heard65 Brab BT7 AUS 12 18m09.271s 1 lap(s)
7 14 Göran Jonsson65 Brab BT7 SWE 7 10m00.019s 6 lap(s)
8 21 Jason Blito Honda GBR 7 10m02.307s 6 lap(s)
9 11 Steve Bird65 Honda GBR 7 10m03.905s 6 lap(s)
10 2 Fulvio Policardi_65 Brab BT7 ITA 7 10m06.009s 6 lap(s)
11 6 Axel Cookie Brab BT7 GER 7 10m12.155s 6 lap(s)
12 7 Billy Nobrakes Brab BT7 GBR 7 10m32.744s 6 lap(s)
13 8 Vlad Vosblod Brab BT7 GBR 6 9m22.441s 7 lap(s)
14 5 Skymole 2173 -m65 Brab BT7 JPN 6 10m09.919s 7 lap(s)
15 9 nigel smith65 Honda GBR 4 5m46.692s 9 lap(s)
16 22 Ray Cattini65 Brab BT7 ITA 0 DidNotStart 13 lap(s)
17 4 Bernie65 Darwin Brab BT7 GBR 0 DidNotStart 13 lap(s)
18 19 2 UKGPL_T7 Brab BT7 ITA 0 DidNotStart 13 lap(s) \
Not to mention you're looking at it wrongly. You shouldn't take the percentage of retirements vs. the number of running drivers at that moment, but the total number of participants, otherwise it makes no sense at all. If we go along with what you said, in the same sense we can have 2 running near the end and if 1 of them retires, consider it 50% and ask for a rerun...
But anyway, 17 started according to my RA export, not 13.