The damage on the first fork was probably the result of riding with a loose headset, allowing the threaded cup to wobble on the threads, eventually eroding them. Unfortunately, this means the threads are gone in the very place you need them most. It can be repaired, but it's more involved than simply chasing the threads with a die. I've fixed forks in that state by filling the damaged threads with brass and then cutting new threads into the brass. The brass threads aren't as strong as the original steel threads, but if you're careful to keep the headset properly adjusted they'll hold up fine in normal use.

I agree the second fork ought to be fine with just chasing the threads.