They have had to make various changes as the process this year isn't quite the same as last year (or the year before etc).
If SGS do introduce an additional pass mark it is hard to see how they are not in breach of the Admissions Code as they have failed to take all reasonable steps to inform parents prior to 31 October (especially when Wilsons and WCGS both did). As I had read their website, and in particular the FAQs about the SET they have explicitly stated that if you pass the SET then:
"For Sutton Grammar School – your son is eligible to be considered for a place at Sutton Grammar School and you may wish to list this school on your CAF. Your son will then be invited to sit our second stage test to be held on Saturday 16 November 2013 to determine his position in the rank order."
This contrasts with
" For Wilson’s School - your son is eligible to sit the second stage Entrance Examination for Wilson’s School details of which will be sent to you by email. The date for the second stage Entrance Examination will be Wednesday 9 October 2013. The outcome for the second stage entrance examination will be emailed to parents/carers by the end of October (in advance of the deadline for completion of the CAF). Please note that success in the examinations does not mean that a place will be offered."
For both Wilsons and WCGS the "outcome" was an email to say whether your son was or was not eligible to be considered for a place. SGS had met this Admissions Code requirement by using the SET.
It is probably all moot anyway, but I think SGS would be on dodgy grounds not to allow a boy who had passed SET, named SGS and sat on the 16th to go on the waiting list. And in the (unlikely) event that SGS has spaces, and there are boys in this category I think they would have a strong chance at appeal.