There are very few startups that need to be in “stealth mode”. If anything, startups need to be more vocal to get themselves on the map and to do way way more customer development.
I think anyone who credits stealth mode with their success probably doesn’t realize they would very likely have also been successful without it.
In my experience, software, business processes, and hardware are best kept close to the vest until sufficient momentum and maybe market saturation is reached.
It does not matter if the item holds a copyright/patent/trade mark; they are post even re-active solutions. It's like an ambulance after a car crash. Excellent if there are good doctors in the ambulance, but better the avoid the car crash all together.
Putting together a team of competent engineers, developers, etc and having them create something meaningful is hard enough as it is. Trying to copy someone else’s tech doesn’t lower the bar all that much.
There are myriad of other examples, or different scenarios where an NDA or non-compete failed, and another company just puts out a product faster and cheaper. Happens with software, hardware, and of course business processes.
[0] https://www.hongkiat.com/blog/amusing-knockoffs-popular-tech...
[1] https://www.buzzfeed.com/alannaokun/30-knockoff-products-tha...
[2] https://www.liveabout.com/hilarious-knock-off-brands-4767601
I don’t see any out there that indicates they beat the original idea to the market by way of breached NDA or non-compete.