I'll try. The only trouble with answering these sort of queries is that even when I do it in perfectly good faith (which I do - as I repeatedly make clear, I am not employed by the Marketing Department), suspicious people accuse me of hiding facts and try to use it as a way of beating Oxford about the head and generally hurling abuse at us on this forum. It is much easier not to respond - that way you don't get dragged into acrimonious and increasingly sterile debates about points of trivia.
That said, I'll answer what I can of Keith's questions.
A standard course isn't 30 students. We don't like taking more than 18 on any one course. We did, when PPSC and 4Fforces failed and we were inundated with demands to help those who had been let down and, greatly against our inclination, ran CBL06, which was more than 20. It didn't really work terribly well, by our standards, and now that some of the Khalifa courses have passed through into the flying phase, we have have been able to find enough classrooms to be able to split them into 06A and 06B, which we think is better.
It isn't typical to give as many as 4 on a course a futher 4 weeks study before they take JAAs. THe way we do it it to split the 14 exams into 2 phases, mainly Techs in Phase 1 (8 subjects), followed by VFR flying, followed by JAA Navs in Phase 2 (6 subjects), followed by IFR flying, including about 50 hours Seneca. Two weeks before each set of JAA exams, the students take a mock JAA exam (which we call School Finals) which we believe is either exactly representative of the JAA standards or, in some cases, just very slightly harder.
We make an assessment of the students' performance on all 8 (Phase 1) or all 6 (Phase 2) School Finals and decide whether, on balance, we think they're going to pass most of them (not all of them). If we think that they probably won't (we let them get on with it if we think they might just fail one or two) we ask them to delay. We give them help and extra tuition - mostly extra private study - they know what they've got to do - but also private sessions with individual instructors. We don't do this to improve our exam percentages - we didn't even start using this for advertising except as an afterthought. We do it in the best interests on the student. We don't want them to have to take too many bites of the cherry in order to pass - the weak ones might run out of numbers of attempts, and also we don't want the 18 month clock to start one month too early if it's not necessary.
To answer Keith's specific points, we don't compile statistics for delaying students by 4 weeks, but my guess is that it's less than 10%.
We don't compile statistics for students who pass everything on first attempt, but my guess is that it's about 60 - 70%.
I would guess that very few indeed who achieve full passes first time have been held back. We don't hold people back unless we have real doubt about their ability to pass first time and so those that we do are weak anyway. Often, they still don't pass everything first time, but at least they only fail one or two, and that makes the re-sits manageable.
The reason that we don't do any more detailed breakdowns is because we don't have any need for this information. Our computer already produces the statistics we quote because it's programmed that way, and it's easy to stick the results on the website. But they are not produced for advertising purposes and so to get authentically correct answers to your queries would mean my going through all the results over the last 2 years to break them down into the format you require. I'm not going to take time to do that - I'm too busy teaching students and re-writing the Oxford Jeppesen notes. But nobody at Oxford has anything to hide and so I've given you a 'feeling in the water' best guess estimate. It may not be completely accurate, but I think that it's about right.
I hope that that helps.