First, well done for taking the decision to retake, especially after what you went through in Y13. It's very brave and commendable, and shows great resilience and determination
It is my understanding that the way the grades will be awarded this year is (a) the school makes a judgement about the grade you would have likely achieved this summer, and (b) the school ranks each student relative to others for who they also judge would have got the same grade.
For part (a), the school would have taken into account all available evidence, including school records, mock exams and non-exam assessments that you have done this year. Were you attending school this year or studying at home? If you were at school, then the school should have enough evidence to make a fair judgement. If you were studying at home, you were still made to sit exam papers to gather evidence. The teachers know you, know all about your extenuating circumstances and will know what you are capable of achieving. But all this aside, they have hard evidence in terms of the papers you sat and for which you achieved A*s, so I would say they used this to help make their judgement.
In reference to the ranking system, if your teachers felt that you would most likely have achieved a grade A in say Economics, and there are 4 other students in the current Economics class at your school that they also felt were likely to achieve a grade A, they will rank you and the other 4 students from 1 (being the most secure and likely to achieve the grade) to 5 (the least likely).
It is my understanding that Ofqual will look at the centre as a whole rather than individual students' past grades. So if a centre tends to have around 6 students who take say geography each year, and the results are usually around the C-E grade mark every year, and then the centre suddenly awards all their geography students only A*s and As this year, this will likely raise a flag. Of course, it is possible that they have had a year where they have very able students, but then I assume they would have to submit hard evidence to support their grade judgement. (There is also grade standardisation which I don't think I need to waffle on about here!)
As you have said that your centre is known for producing good grades in the region, and it sounds very robust in its gathering of evidence, I would say that it wouldn't be out of character for them to award high grades each year?
So all in all, try not to worry too much (I know that's easier said than done!). If necessary, you could sit the exams in October. Would this be an option for you? If so, continue to study/revise until the A level results are published, as then you have that option should you need it. But regardless of your grades, be very proud of yourself for having the determination to resit.