Saw this on a tutoring website
At 11 plus, Wimbledon High accept around 100 girls into their Senior School. Of these, 40 will come from the Junior School while the rest come from a variety of state and independent schools. The ratio of applicants to offers tends to be 10 to 1, however this is subject to change and can go as high as 20 to 1. Despite not having an official sibling policy, sisters of girls currently attending Wimbledon High will be given preference when up against an equally strong applicant.
They also state that they usually cut down numbers by half after the first stage, which seems to agree with the poster above.
I’d there are only 60 places and there are 350 in the second stage, I doubt they would have such a long waitlist.