C vs S did not strike out on the basis that the abortion was lawful, they tested the criteria of the 1929 act. This was because any abortion on socio-economic grounds of a viable foetus was unlawful and while there was an upper time limit where the foetus would be deemed viable there was no lower time limit
The court ruled on the age of viability of the foetus. Nobody had been foolish enough to claim before that, at 21 weeks, a foetus might be viable. The man who brought this case was laughed out of court. But to stop any other idiot doing it again, they changed the law in 1991, to bring in a fixed 24 week time limit, so there would be no doubt in future about the time limit. I would imagine a 10 year old could understand this.