Well, in my sister's time at JR (7 years ago) the median UAI was 99.3 I think? But then she said that after that the UAIs were collected voluntarily from students and of course if you get a shitty UAI, you're not gonna tell Ruse... so future years may be distorted.
As for the lowest UAI- that's also not true (that it's 97). There are a few people who get below 70 in JR, IIRC my sister also said if your UAI Estimate <90 you had to talk to Mr Quinlan (the Principal of the time- not sure if he's still there). As for other selectives, there's always a couple of ppl who take the HSC as a joke and end up with 60, 50, and I think two years ago there was a 38 in my school. It sorta annoys me that these ppl take up a perfectly good spot which someone else out there really wants and would've made use of- if there's one thing I've learnt from new students in yr11, it's that they are really dedicated and can whoop our asses >_>