Can a syllabus be adopted and modified?
In some cases, it could be that the instructors had a template provided by the school.  When I was an instructor at a college, I was required to update a few things on the syllabus, like my name, but I was required to NOT change ANYTHING else.  I had no flexibility (in that one specific way...  I did have a whole lot of flexibility with just about every other way that I ran my particular class, which I know is quite different than what some other instructors experience).  One thing I did have the flexibility to do was to create my own addition to the syllabus, but the college bureaucracy, which determined the official course objectives, also mandated a certain amount of information get presented unaltered.

In that case, I, as the instructor, never bothered to check the copyright of each and every syllabus, because obviously I had the organization's permission to do what the organization absolutely required of me.

This is just one example: The main point being, in some cases, instructors might not be creating their syllabus entirely from scratch.  Surely, the specific details vary from school to school.