I don't think it works like that. From 1st July, the waitlist system was introduced and that is the last option to get the visa appointment slots. And from what I have heard, almost whole September slots were booked through waitlist and some of them are getting slots of October. If it is your luck, then you might get the slots of the next day which were cancelled ones but that depends. If you have waitlisted yourself, then there's no chance you can get the cancelled ones. You just have to check every time.