Problem: Editor event listeners do not recognize added layers
The Editor events OnChangeFeature, OnCreateFeature, and OnDeleteFeature will not listen to row changes of layers that were added to ArcMap after the edit session was initialized.
Custom tools or editor extensions can listen to Editor coclass events.
Solution or Workaround
When listening to the row events (events propagated by geodatabase feature classes), write a class extension that implements IobjectClassEvents to overcome this limitation.
The geodatabase section of the developer samples contains a class extension sample that listens to row events.