New Standard is followed for all the Adaptive Forms. In addition to that for XFA based Adaptive Forms old standard is still followed, but in that case if you have dropped some fields form the sidekick and not from the Data Hierarchy tab, those fields will not be pre-populated. So as an example, if in your XFA based Adaptive Form, you have used only XFA based Fields then the following two XML structures are equivalent for pre-populating
But if you have some fields that are not bound to XFA, then in that case the second structure will not pre-populate those fields.
Hope I have answered your Query