I think you will find some T1s caught early enough can start on oral; my great niece needed insulin to recover, is currently on oral, but with insulin in reserve. She has a test meter from the NHS and been warned to expect her pancreas to give up. The English hospital has confirmed her T1 status from C-peptide and GAD antibody tests and she is documented as T1, under a hospital D team.
Slight digression, she was travelling in Italy when she fell ill and very much to Italy's credit that, as well as hospitals with phlebotomy clinics, they have "drop in" pharmaceutical laboratories where you can get a battery of blood tests done for very reasonable prices; it is how my own jaundice was analysed and assessed as Pancreatic cancer. It took an English hospital 6 weeks after my return to confirm the analysis that they were given from the Sicilian laboratory, which was ignored by the hospital who preferred to do it all again and waste valuable time, as well as leaving me untreated, not even having my bile duct by-passed by a stent - for 6 very stressful and worrying weeks. I had no idea jaundice could reduce someone to such a zombie state; it was taking me 2 hrs, with assistance, just to get out of bed, dressed and downstairs, where I was uselessly drifting in and out of sleep in an armchair, rather than bed. I couldn't even answer the phone!
Rant over, I agree it is unusual to not start on insulin. And of course those misdiagnosed T1s have survived on oral meds until they get the more appropriate insulin treatment.
I was more interested that the OP's dietician didn't on the face of what
@Charl has stated, didn't understand the fundamentals of D. Perhaps she saw something else on the medical records that triggered her observations.