You also might not see all fields from your source system if the filter options have been limited to the pre-defined filters by a Dashboard editor.
Furthermore, you might see some filter values which you can filter for, but don't see any data as a result. This means that there is
a) no data for this filter combination in your source system or
b) you don't have permissions to see the resulting data.
For any questions on permissions, please speak to your account admin.