The waiting list is still in operation until December of Year 7. In any given year they will offer the place to the next child on the waiting list. For an idea of how low the score has already dropped since March it is best to look at the waiting list threadviewtopic.php?f=11&t=41539
The score for KEFW has already dropped several points. For CHB, approximately one third of the year got their places from the waiting list after March 2nd.
The thread above is for the current year. For last year there will be a separate thread somewhere which you can search for.
There are separate waiting lists for PP and non PP children as the schools have to maintain a certain proportion of PP children within the year group.
From January of Year 7, children are retested in line with the "In Year Admission" policy.
When my DD was in year 7, several girls left and were promptly replaced. This caused a knock on effect at the schools they came from (Handworth Girls, KEHS etc). For KEFW, as it is co ed, places could be made available from children moving to another Grammar (boys or girls) private sector or out of the area altogether (as in the case of the girls who left from my DDs year as several emigrated to other countries).