Edited to say this was meant to be @ArseInTheCoOpWindow
My son is similar. Currently year 13.
Undiagnosed ASD caused school refusal and a complete mental health breakdown. He couldn't access formal education at all years 7 to 11 and barely accessed any form at education for approx 3 years. Despite this he made it back to state mainstream for A Levels having self taught for 6 GCSEs.
He did put all of this information on his UCAS form & had specific teacher references pointing this out and applied to Oxford and 4 other (all Russell group) universities with a 3 A* at A level prediction having done amazingly well in year 12.
He did well enough in the admissions test to be interviewed at Oxford, they don't interview those who don't score highly enough, but wasn't made an offer. He was fine with that. The process was enough for him. To have done well enough in the test was reward in itself for a child from his background.
He has 4 other offers but none of them are contextualised despite having more context in his education that most children I would hazard a guess! Conversely we know children who've had no gaps in education, spent some of it in independent schools but have had contextualised offers because their parents have split up and they live in a poorer postcode area. We're not rich ourselves by any means!
I just wanted to clarify that having clear detriments in education, missing out on 5 years of it, did not result in any contextual offers for my child.
He has an offer for UCL. If he manages to get the grades despite all of his disadvantages then I would say it's a marker that he has a level of natural intelligence.
I think we can all get very hung up about which is the most disadvantaged in terms of university admissions. Everyone takes it personally. Ultimately most kids end up with the degree & career they deserve. Parents seem to be much more hung up about the Oxbridge brand than the kids as far as I can tell.