The Unloseable Pencil That Got Lost

This little 4" ring top pencil was rattling around in the family junk drawer; I couldn't decide quite what it was meant to be.  It didn't have a ring, so I put a jewelry jump ring through the hole in the top.  It looked contemporary, that is, contemporary to me (read that as "vintage"), and it worked just fine, too, but it seemed lost and forlorn.

Then I saw this:

FOR SALE PAT PENCIL.  IT DOES WORK AND HAS A BUILT IN RETRACTABLE CHAIN.  I BELIEVE THIS IS FOR NURSES OR DOCTERS BUT CAN BE USED IN OTHER AREAS OF WORK.  VINTAGE ITEM.  SAYS ON THE BACK of THE PIN:  KETCHAM & MCDOUGALL.  

DIRECTIONS FOR USE:  FASTEN YOUR PAT PENCIL TO YOUR CLOTHING WITH THE PIN POINTING DOWN, NEVER CROSSWISE.  TO OPERATE, PULL OUT THE CHAIN AND LET IT RETRACT SLOWLY UNTIL IT CATCHES.  TO REWIND, PULL OUT THE CHAIN AND ALLOW IT TO RETRACT QUICKLY (JUST LIKE A WINDOW SHADE)  TO REFILL THE PENCIL, TURN THE POINT IN THE OPPOSITE DIRECTION AT LEAST 3 FULL TURNS.  INSERT NEW LEAD AND PRESS INTO THE CLUTCH.  FOR ERASER AND EXTRA LEADS UNSCREW CAP.

SIZE:  THE PENCIL ITSELF IS APPROX 4 INCHES
COLOR:  SILVER AND WHITE
CONDITION:  USED WITH NORMAL WEAR BUT LOOKS BRAND NEW.  BOX HAS SCUFF MARKS.

The unloseable PAT pencil!  Now that I had a name I could look for others, and I found a black one, too.

Pin-on pencils have no doubt been around for a long time.  There was one made of brass and brown celluloid in my great aunt's things, unmarked by any maker's name. Unlike PAT, it has no place for a ring in the top, the wound-up brown cord goes directly into the pencil.  You can see that it winds around a little wheel inside the round case with the pin on the back.

But when a pin-on pencil loses its pin, is it still a pin-on pencil?  And how did an "unloseable pencil" get lost?  There must have been a weak link somewhere in that retractable chain.