Hi @Victor_Sava, welcome to the Asana Community Forum and thanks for sharing your feedback with us!
As it stands, only tasks and subtasks with due dates that are associated with the project will show on the project Calendar. If you want to see which tasks your team worked on a specific timeframe, I recommend you creating an Advanced Search report. You will also be able to see the list of tasks that have due dates in the report in Calendar view.
If you want to have a specific section in your project where you can track user activity, I recommend you adding your vote to this request:
I hope this helps! Let me know if you have any other questions