I see that you were asked in a previous post about testing for secondary endocrine conditions that can cause insulin resistance, specifically acromegaly and IAA (insulin auto antibodies). My girl had both conditions. We suggest that people get their cats tested for these conditions when the dose gets above 6 units. Although there are cats with those conditions on less insulin, the chances are very high that a cat on six units or above has a secondary condition.
There are reasons to get a kitty diagnosed. First of all, there are treatments for acromegaly but you have to know the cat has it first. The latest research shows about one in four diabetic cats has it. Second, there are also side effects that come with acromegaly which is caused by a benign growth on the pituitary tumour. Knowing to look for side effects means you can treat those too. An example with Neko - her vet saw a red mark near a tooth and though that tooth needed to be pulled. I went to a dental vet, and he discovered the red mark was due to soft tissue growth on her gums (caused by acromegaly) and the tooth above was rubbing on it. The vet shaved the tooth, Neko didn't have to have it extracted.
Third reason for knowing the cause of the need for higher doses is we can tweak the dosing to get Kole to better numbers faster and to respond to how his dose needs might change over time.
With later nadir cats, you have to get used to shooting lower numbers. Neko would occasionally show me her nadir at PS time.