I've made a serious error by not identifying one of the filters.

The correct selections for the balance of the races are:

Ipswich
4/2
6/10, 11, 12
7/10, 13

Mornington
6/9
8/5, 10

Mt barker
2/4, 5
7/12
8/4, 8

Mildura
5/5
6/10

Mudgee
5/1, 3
7/9

Nowra
5/5, 11
7/ 3, 7, 8, 11, 12
8/4

Pt Lincoln
2/1, 6
4/6
7/6, 13

Canterbury
3/9
7/14

Moonee Valley
6/3, 4, 5
7/2, 4, 10