The concrete derived AssocPersSubentityId class that simply keeps the SubentityId when it is persistent and does not change.

Autodesk.AutoCAD.DatabaseServices.AssocPersSubentityId
    Autodesk.AutoCAD.DatabaseServices.AssocSimplePersSubentId

Public Class AssocSimplePersSubentId
Inherits AssocPersSubentityId

public class AssocSimplePersSubentId : AssocPersSubentityId;