Datasets and dataset collections are both collections. However, one difference is that while it is not possible for a dataset item to point to a non-existing item version, it actually is for a dataset collection items because there are "draft" datasets (while there are no "draft" files).
The currentVersion property for a dataset actually refers to the Draft version. Therefore the "real" latest version of a dataset is currentVersion - 1 (unless there is only a draft version of 1).
Datasets and dataset collections are both collections. However, one difference is that while it is not possible for a dataset item to point to a non-existing item version, it actually is for a dataset collection items because there are "draft" datasets (while there are no "draft" files).