There are two ways to add student numbers
1. When creating or editing a list, these are list based student numbers
2. You can upload student numbers at module/unit level as described here in the Hierarchy data format article.
The two sets of numbers are record separately in the data and one does not overwrite the other.
When the system refers to the student numbers but in Reviews 2.0 the expected behaviour and by design that the list numbers have precedence over hierarchy uploaded student numbers. Only if student numbers are missing at list level will the, module/unit level numbers be referred to.