Can't help thinking that if some can sit the tests and some can't, then there is the potential for positive discrimination benefitting those who couldn't..
Child P1, although predicted AAA, is a middling candidate when compared to Oxbridge applicants as a whole. He couldn't sit an aptitude test due to Covid.
Oxbridge admission officials have no evidence that Child P is a middling aptitude candidate.
Child P2, predicted the same AAA is an equally middling candidate applying for the same subject, but is able to sit an aptitude test thereby giving Oxbridge admissions officials evidence of their "less than top drawer" ability compared to Oxbridge applicants as a whole.
In an effort not to prejudice Child P1's chances, because allowances need to be made, it wasn't their fault they couldn't sit the aptitude test, there is the risk that they benefit from not having had to demonstrate their actual ability by comparison to their peers (aka "competitors").
So long as someone doesn't say "I know !, We'll write an algorithm to sort the situation out."