Why would they state the obvious? With all visa requirements are mentiond without explicitly mentioning a duration of the requirement because it is obvious the requirement is for the visa itself and not just for the application process. Everyone with common sense will understand.
It is easy to say when something is not according to your expectations, it is just trolling. What you present as facts is just cherrypicking, only what you like is true, the rest you consider trolling.
If you don't believe IO might check for complying to visa requirements, just ask yourself at Immigration or MFA. It just is their task. Chances they will check at the border are minimal because it takes time and there are other priorities.
When you ask MFA or Immigration, they tell you, you should comply with all visa requirements at each entry. So you indeed don't need to enroll on any subsequent course, but if you don't you are not allowed to enter. The fact that this normally is not enforced can change any moment, or might never change.
Technically the visa is only valid to enter the country as long as you comply to the visa requirements. IO can check at each entry if you comply, but currently chances are almost zero it will happen.
I did not hear of any checks on really attending the course, and also have no idea if they ever will do this.
For ED visa this did happen in the past, but I think it is rather complicated to do so.
But checks you are really enrolled are more easy to implement of course.
Not complying wit visa requirements is a risk everybody has to decide if it is worth to do so.