The legend (true? false? dunno) is that first year grad classes used to be "open": anyone could sit in. But only a few would be allowed to pass the exams to be "admitted," for Yr2.
When I was a first year, the rumor was they wanted 30 second year students, but consistently had abt 40 taking the first-yr exams...
A few years later, they got it to 30... and passed abt 20. It was just A Thing, apparently.