Any work you do as part of your tasks as an employee of an organisation in the Netherlands belongs to your employer, not to you, as they are paying you to do the research/work. This means that anyone not working at the university (which may include yourself in the future!) needs permission from the University to work with the data and code if it is not publicly shared under an open licence.
Copyright means that we determine how the work can be re-used by others, and what rights they have in copying, modifying, and distributing the work. When we do not explicitly formalise these rules in a license, the code and data cannot be freely reused by others. This is why licenses are so important!
More information
- https://www.tudelft.nl/library/copyright/teacher-copyright-answers#c1132165