There have been significant changes to the important dates data at the University of Waterloo. The underlying model for it is changing in the WCMS system where it comes from. The good news is this means that the concept of important dates will expand to more areas!
The new data is available in the new version of the Open Data API. The end point is https://openapi.data.uwaterloo.ca/v3/ImportantDates and you can find additional information and documentation here https://openapi.data.uwaterloo.ca/api-docs/index.html
At this time we will not be back porting the data into the existing v2 version of the API. This means that new dates and changes will only be reflected in v3 and you should update any use appropriately.