The limitations of ground based radar are just that, limitations. There are a multitude of factors that come into play in regards to what you can and can't see as a radar return.
I used to work out on the top left coast. We every so often we would get phone calls about aircraft that we weren't talking to, and couldn't even see (no primary return). Sometimes, eventually there would be a blip or two - but most of the time there wasn't. Point is, they didn't want to be seen. And if they were, it was because they had made a miscalculation which allowed it.
That being said, just out of curiosity, what is your definition of a "working system?" I'm not trying to pick, I'm genuinely wanting to know. This community is comprised of mostly adult professionals who contribute to this system and want to make it safer and better. That being the case, what is a "working system" when there are people out there who use that system but don't share the ideals and goals of the majority of its users?