Type 1 diagnosis changing

On the positive side being a type 1 or 1.5 will get you access to fsl so don't be in a burry to change that officially.
It is possible to still make insulin, evinced by the c peptide test so check that result, even if your beta cells are dying. So you could be a type 1 going through the 'honeymoon phase' in which case I'd be eating low carb in order to preserve beta cells.
Similarly a type 2 would also have insulin and in the early stages of type 2, you have hyper amounts due to insulin resistance but latterly the fat around liver and pancreas cause the beta cells to produce much less than is required. If you had had type 2 for years but undiagnosed that could be you? Other than being overweight on diagnosis do you have any other markers eg. parent/sibling with type 2, hypertension and high ldl c but low hdl c and high triglycerides ?
i also think your weight loss might be a clue too - have your blood sugars improved ? Do you need less insulin to keep bgs in range? As a type 1 I'd need a little less but for type 2s on insulin some of those people have a dramatic drop in the meds they need for bg control.
It is important to know your type as the pathology of type 1/1.5 is very different from type 2 so I am just wondering if your weight has confused matters as you don't fit the type 1 type so I hope after checking your blood test panel for those c peptide , cholesterol and triglycerides you will have a better idea of your metabolic health. and more importantly what to do going forward with regards to diet (the game changer no matter what type you are!)>

I would focus on getting the weight down if possible by having a low-carb diet. Then it would make it easier to aid the correct diagnosis. You may also find you need less insulin if you are a T2. Lack of natural insulin usually causes weight loss as the carbs can't be metabolised.

As far as I know having diabetes plus positive antibodies equals a T1 diagnosis.
It's not unusual for it to progress slowly enough to still produce insulin after a couple of years.
I had a C-peptide test some 2 years after my initial diagnosis showing I still produced insulin, just below the low normal threshold. Based on symptoms I'd had diabetes for 1 or 2 years before that diagnosis too.

Being overweight doesn't protect you in any way from developing T1.
I was diagnosed with T1 with a BMI of around 36.

I carried on producing some insulin for at least 4 years from a c-peptide test (diagnosed in 40s)

Rapid weight loss is also a clue for T1. Saying type 1.5 are usually skinny depends on your starting weight. I lost a stone but I was just 8.5 to start with