Things do change. The calendars on here do a little more than the ones on the school website.
Before an event, they are what I use for laying out a schedule. I might only put the name of a lecture or activity, I sometimes put down the resources that we will need. The closer the event becomes, the more likely it will be.
After an event, I will often add notes describing what happened in class. This could include where we concluded a lecture, what problems were assigned, or interesting updates. Even if additional details are not available, past events will help us all remember what took place. They should be accurate and reliable resources for us all.