How is this coronavirus different from other coronaviruses? at what point is a coronavirus labeled "novel"?

Novel=new: There have been corona virus strains around for years. Their label comes from the crown like projections about the body of the virus. They do have the potential to mutate/change structure/gene component over time. The covid-19 is just a newly found (novel) strain first detected as a cause of human disease in 2019.The name is just a combination of corona/virus & 2019 = covid-19 for short.

Novel: The COVID 19 virus is named SARS- CoV-2. It is novel because prior to 2019, we had never dealt with this virus. Our immune systems are naive to this virus. In 2003, SARS-CoV was a novel virus. It was new at that time and led to the Severe Acute Respiratory Syndrome outbreak that broke out in Asian.