Hills Please don't spend your time raking through years of negative emotions.
Diagnostic reports will be on file with whoever did them. If it was NHS, then it should be easy to obtain a copy.
Ditto private especially if you can remember the Consultant's name, the NHS don't usually add private reports to someone's GP records.
Your DS will have two NHS sets of medical records, GP medical records and hospital medical records.
He will have to request them, (you can complete all the forms and obtain them if he is under 16. If he's older, do what you can with the request and get him to sign or grunt on the phone that he understands what you're doing as his appointee. ) usually there are details on your GP and hospital websites for obtaining them.
Some let you make an appt and you can have copies there and then, do check.
Nowadays they are free because of GDPR, when I needed DD's I had to pay about £80 to GP and again to hospital.
I echo speakout's wise words, you're doing yourself no favours getting so emotionally fraught.
Right now, all you need is the correct diagnostic report, it's only a small pile of papers.
Then emotion contained in what's written there has already been gone through at the time. Hard as they are to read because they only focus on deficits and not the whole person, try and think that you're presenting this evidence about a stranger who needs written evidence to be able to be seen to have difficulty in certain areas.
Detachment from the emotions surrounding things like this can help you to cope. It's not easy, but it is possible. 