> My other half gave him a little bit of chicken skin a few months ago
Which could have caused an excruciating death.
As long as your boxer is allowed NO fat in his diet (think religiously fanatical about it) and definitely not any of other dogs biscuits, you will give him a much longer life. My bitch was allowed once a month ONE low fat dog biscuit (tiny size), and she would never have survived all those years if I hadn't have been so strict about her food. When the others had treats, she had a bowl of steamed vegetables.
Once you have him on his properly fat free diet, you will be able to give him the odd
tinned Chappie meal which he will love as a change from ID.
(Been there, worn the T-shirt!) :-)
> The only way you will find out is to experiment

A wild and sweeping statement, which I have to totally disagree with - anyone who has no in depth knowledge of pancreatitis would do well to take expert advice rather than "experiment". It's the dog that will suffer the pain - and pancreatic pain is not mild.