The Rarest Campagnolo Dropouts?

It's time to get the Boulder Bicycle Blog up and running again!  

Today lets look at something really uncommon for you Campy fans.  On a recent trip, I found a pair of Campagnolo dropouts that are plug in style.  I've looked on the internet, and a simple search does not bring up any photos of them.  If you go deep you can find an image here and there.  But these are obscure.  Some very famous framebuilders I know have never held them.

Why am I so fascinated by these?  Well, in the late 1970's when I started thinking about framebuilding, I thought silver brazing was great (and easy) and brass seemed difficult.  Plus, if you were a user of Reynolds 753 (not me) you were told not to heat up the tubing to the point where brass would flow, while at the same time you needed to do something to put those dropouts into place.  So a plug in dropout that doesn't have large gaps to fill like a typical dropout requires (enabling the use of silver braze material) seems like a problem solver for sure!

Look carefully below at the braze gaps on a Team Raleigh 753 frame - even Ilkeston had difficulty.  

So the Campy plug in dropouts were a way to use cooler-melting silver.  It also speeds up the building process too.  That's why so many builders went to the easy-to-use plug in style when other companies started making them. 

The shape of the Campy plug in dropouts is a bit weird - Mark Nobilette says it's kinda Swiss looking.  Maybe Campy looked at the back of a Teledyne Titan for inspiration?  Below is a Teledyne rear dropout.

So if the Campy plug-in dropout is so cool and such a problem solver, why don't we see these more often?  I'm wondering if they had reliability issues.  Unlike typical Campy dropouts which are forged, the plug in style is cast.  Maybe the sharp edges led to some failures. 

Perhaps someone knows more and we'll see some info in the comments!