Using vba to determine which model is the default

I am trying to use VBA to rename the Default model within a series of existing dgn files, however I can find no way to isolate it.

The only obvious difference between the Default model and the other models is that the Default model cannot be deleted.

I could find the Default model in a file by deleting each model in turn to see if it throws an error, then undo the deletion if it doesn't.

The one that throws the error is the default, but that's a pretty crude way to do it.

Because the Models Dialog box tool bar grays out the Delete command when the Default model is selected, there is obviously some way to isolate it.

Can someone please advise how to do it cleanly.