And licenses are the easiest part. Scanning for occurrences of copyright notices deep down in the directory tree is usually more burdensome, because every singly file could contain a new copyright owner.
In theory, it could also contain a new license, but after your project has seen n license texts, it is increasingly rare to see the n+1th license text. Because there are far more people and combinations of people that license texts.
In theory, it could also contain a new license, but after your project has seen n license texts, it is increasingly rare to see the n+1th license text. Because there are far more people and combinations of people that license texts.