Hi
First time, I've replied on a forum. I've had T1 for over 35 years and I went to the doctor prior to covid, just to get my medication reviewed, she thought I was skinny, weighed me , just over 9st. But to cut a long story short and numerous tests & scans, my diabetes nurse suggested a test and found that I've PEI now. Now with the right drugs Creon 25.000 4 with every meal I'm now back to 11st. When the diabetic nurse told my doctor, he admitted that he'd not heard of that.
Maybe your dad can ask for that test
Steve