If you are permitted to use data from other parties, you will have to account for those as well if your research is to be verifiable and reproducible by others. You may recognise this from chapter 1 of this course: Data collection: Discover existing data, weblecture ‘Assessing usefulness of research data of others’.
You have the following options:
If the used data is preserved correctly somewhere for the coming ten years, refer to the data repository in question.
If it is not taken care of, contact the responsible persons, negotiate correct preservation in a data repository for ten years, and refer to that repository.
If this isn’t possible, try to arrange a local copy that you preserve yourself;
If this isn’t allowed, you will not be able to present the data in case of questions. Therefore, you should question yourself whether you can actually use the data.