I am the one that actually caught the first fluctuations but at the time of diagnosis I was waking up to 10's and commonly going into the 16's after eating when they decided I was a diabetic and a type 2.. Even before my BG's starting climbing I swam 75 laps a day in a gym pool, I was/am a strict vegan and ate very healthy. But I was overweight, not "obese" but overweight which is why I believe they just assumed I was a type 2. And I asked repeatedly if I could be a type 1 as I had an uncle that had died from being a type 1, but they never tested me, just kept insisting I was a type 2. It wasn't until I switched doctors that I was tested and properly diagnosed.
One thing they say points to a misdiagnosis is that within the first 3 years you need insulin to control your sugars. I wasn't even put on insulin for 5 years. So obviously it can be longer. Medications can help at the beginning, and changing diet only because you still are making some insulin sometimes for 8 years or more. You eventually have to have insulin as a type 1
I was very lucky and seemed to have escaped any complications from being misdiagnosed.. Of course some of any complications unfortunately could show up as issues later in life.