I have been following this post, watched it go from the specific to the general then back and forth. It all revolves around the intent to deceive. Is it the intent of a call maker to copy another and deceive the public into believing the design is his? That's what must be proven.
If someone said " If I could do it the way you do it, I would do it that way!" and he did it. That's' intent. Now how about he gave you credit for the idea. Now what?
When two call makers come up with the same idea independently and make calls using it. Is one going to stop? It would be ludicrous for one to do so. Does each have to prove it was their original idea?
How about the x-ray issue. Museums do it all the time to learn history so they can make replicas and not destroy the originals. Same deal for calls. I don't think we want to cut up or clean an old yelper stuffed with cobwebs. We would never know that the infamous "Clucker" had hand chased threads or even came apart at one time, if a dentist had not volunteered his high tech machine to peer inside. What was the intent?
Remember intent to deceive must be proven. Is it worth it? Do you have the resources to do it and make the other guy stop or pay up?
The Geezer