There was one update where the leapfrogging got so bad that SB offered a Combi licence so that Nuendo users could open Cubase projects. Unfortunately it all went horribly wrong when it was discovered that not only did the people in the US get two separate licences, whereas the UK only got a combi, but when the update for Nuendo finally came out it would overwrite our Cubase licence, thus making it a temporary licence, at best. Oh, and it wasn’t free either. 
DG