NAST table - entries without object key

Hello,

I'm seeing 35 entries in NAST table without any object key linked to it.

This is resulting in multiple output types for any new object - e.g. For any new PO, there close to 20 output types, which are are not related to any of the data from PO.

Questions : How can an entry get saved in NAST without assignement to object key? Can we delete these entries ? How we can make sure, this dummy entries dont regenerate once deleted ?