Yes, I agree with all of the above ie if folk are insulin resistant, then initially their pancreatic beta cells produce more insulin than usual to try and compensate; the greater insulin secretion might not be enough and hence the diabetes, and this is the major point. The body makes insulin by splitting pro-insulin into insulin and c-peptide, but when producing extra insulin, the split doesn't always happen at the usual place, and these other varieties of insulin don't work quite as well. C-peptide lasts in the blood stream longer than insulin (half life about 6 times longer) and accumulates if renal function is a bit impaired. The fact that the C-peptide level is up shows insulin production, but does not per se mean that medication needs to be increased; however, if medication needs to be increased (the HbA1c was high), an agent that sensitises the body to insulin would be a better bet than flogging the beta cells with more sulphonylurea.
Intersting question
best wishes