Side Window Quandary - What is the 'duck-shaped' metal piece?

[Namerow]

The picture shows the driver-side window glass assembly taken from a long-gone 72 Z.  If you look at the bottom-right quadrant of the assembly, you'll observe a stamped-metal piece bolted onto the near side of the glass.  It looks kind of like a swimming duck (ok, maybe a loon), with the beak pointing to the right.  With the glass installed in the door, this piece would be on the outboard side of the glass.

Question:  What is the purpose of this stamped-metal piece?  It doesn't show in the parts fiche drawing and I don't see in the FSM drawings either.  In addition, the side glass from the 70 Z that I'm working on doesn't have this piece either.  The 72 donor from which I took the window assembly was my daily driver back in the 1970's and I'm 99% positive that this is the glass that was installed at the factory. 

Is it some kind of brace or reinforcement for this part of the glass?

Or is it an anti-'Slim Jim' theft-deterrent piece?

Is it a factory piece? (It sure looks like it).  If so, when did these start to get fitted to our Z's?

I'm trying to decide whether this something that my 70 Z would benefit from receiving as a transplant.

Edited April 2, 2016 by Namerow
comment & #2 picture added

[grannyknot]

I don't think Nissan started including that piece until 71, it wasn't on my car. I assumed it was just some extra support for the glass but the anti slim jim is an interesting idea and has some merit.