My nephew, Tom Travis - a professional fly fishing outfitter, fly tyer - and I were just having a conversation about this very subject last evening. We both have seen numerous patterns come and go over the years - patterns that were hot for awhile and then just disappeared. The reality is that they worked then and they would work today but no one uses them. I can't imagine a fly pattern that, if you fished it often enough, would not catch a fish. However, that being said, there are certainly some patterns that will catch more fish, more consistently. I think most of us have fly patterns in our boxes that we have not used in years and some that we have never used. That does not mean that they would not fool a fish but we have chosen to use other patterns. When was the last time you used a Cowdung wet fly? How about a Royal Coachman dry fly or a wet Adams? Would they still work? I think we all know the answer to that question.