On the bolded part, I don't think that'll be the case. The coming 9th Circle group are liable to be a much larger group than normal, but according to Kumi there are tens of thousands of 8th Circle members of the sect. There are a thousand 7ths at most at any time, though maybe a few less every now and then as someone dies or leaves the sect, but they promote up to fifty every year to the 6th, and those would tend to have longer lifespans than the members of the 8th due to higher levels of cultivation so I'd expect there to be thousands of people who are in the 6th or up.
Now, while the sects have apparently been lax in their testing duties lately, they still do regularly test and bring in a crop of new disciples twice a year. I'd presume they're normally testing within a certain age group to make things easier. Even so, the Delving Heart brings in hundreds of disciples twice a year, as do the other six sects. So there's still a very large percentage of the population who have been tested. There are just places where people are slipping through the cracks. The current testing will look at people regardless of their age range, ensuring anyone who isn't on record as having been tested gets testing. I'd presume anyone who gets tested who isn't of the right age to go to the sect will simply be scheduled to do so when they're old enough, though anyone found who is older than the norm will be sent.
So I don't think you're going to see a 9th Circle so large that it'll be anywhere close to enough to eclipse the existing population of the sect. Personally, I expect the incoming 9th will probably be something like triple or quadruple the norm. Maybe a bit more, but still in the low thousands. Still rather daunting to manage given that'll be a much larger burden on the sect than it usually would be, especially with regards to the Elders having time to give lessons to them and giving out Sigils.
) then if you have questions ask them! If you tag me I'll answer for you 
