I have no religious, ethical, or allergy reasons for not eating certain items, but I can certainly appreciate the dilemna of those who do. Two episodes.
My daughter has an extreme allergy problem, one of which is peanuts. At one point, she ate an M&M, and immediatly started breaking out. Checking with the manufacturer, we learned that they did indeed vary their oils based on availability and price. I don't know how anyone would know of changes such as these.
Second incident. I recently ordered takeout chinese from a restaurant with which I had been dealing over several years and that had now changed hands. Ordered something with lobster in it. Instead, it had crawfish tails. The new owner denied any change. But I can tell the difference. Have not gone back.