How the first abortion happened is irrelevant with your idea though, it doesn't matter if the woman was young and just straight up didn't use contraception or anything like that, all that matters is every abortion after the first. It's been a pain in the ass to find stats for repeat abortions in Australia (for reasons you already know), but I was able to find a study on contraception use in relation to repeated abortions for the US and apparently women who have repeated abortions are just as likely to use contraception in general (54% for first timers), and are more likely to use a highly effective method like the pill or injectable, and those using the pill are something like 25% likely to be using it consistently. Assuming similar rates here (and I have no reason to assume they wouldn't be), that doesn't strike me as an incredibly low statistic.