I started feeding 35 years ago and crows never touched the suet until a couple of years ago.

By the way, in downtown Rochester, every winter thousands of crows roost in a small area, I'd guess in a rough square about 200 yards by 200 yards. Their droppings create a lot of problems and every year the city spends about $25K trying to scare them off by various methods. I don't really know how much success, if any, they have.