I think i can answer this:

Netservices are unique. They are generated here:

https://github.com/xbmc/xbmc/blob/master/xbmc/network/osx/ZeroconfOSX.cpp#L65

and put into the map here:

https://github.com/xbmc/xbmc/blob/master/xbmc/network/osx/ZeroconfOSX.cpp#L122

Thats it ... one service can only exist once in the m_services map.