Taking one's life in one's hands, but...
On the point about,every year, people apply with grades in hand- yes, of course they do. However, normally when they do this, they will go through the whole application process and be in competition with the normal chronological year's cohort. Their grades judged against the predicted grades of that cohort, their PS ditto, their interview performance. If they get that far. and there's the difference - in a normal year, even those applying with super grades on hand may not do well enough in that year's competition to get a place. No one says,well, if they'd been competing with their chronological cohort, they'd have been in, so even if this year's chronological cohort is stronger overall, we'll give them a place regardless?
This year, of course, that group will be those applying with suitable CAGs in hand. Plus new 'year 14' applicants taking the October exams (who presumably will have what amounts to an unconditional if they get an offer in January, if they have already met their offer grades by then).
However, this time, there will be a number of applicants who will essentially get 2021 places on 2020's performance. The only part of the process they will have to go through is getting the grades for their existing offer. Which in a normal year would have ceased to be an offer at all on results day, when they didn't meet it. This may turn out to be only a handful overall, but worst case scenario, could be most of the 'over offer' contingent. After all, they were predicted to get the right grades back in September 2019, just as those whose CAGs subsequently met them. (Note, Cambridge puts no conditions on whyone's CAGs 'failed' - thei Admissions page info doesn't say that it has to be due to the nasty, unfair algorithm, it could be that one's originally A* predicting teachers saw subsequent falling off of effort / performance sufficiecint to make their assessment only an A and the algorithm merely agreed).
It's this 'unknown' that is the issue.