My husband has had a similar experience. He too had stage II pancreatic cancer and had a distal pancreatectomy/splenectomy in Feb 2024. Initially his glucose was fine. They did not test for a year. In Feb 2025 his A1C was 8.4. He is now on 1 g of metformin per day and doing pretty well (A1C of 7.1). they did not totally blame his diabetes on the surgery but also on the high doses on steroids (from chemo and other issues he has had), he is 68 so they said it could also be age. I don't think they can tell you for sure the reason, but I agree, it seems obvious if you are missing half your pancreas you might end up developing diabetes!!