I am advised quite a few in collector hands have pin or staple holes in each corner.

These had evidently been roughly affixed to lobby notice boards etc, with thumb tacks, for the display purpose they were sent.

Others appear to have been mounted in frames to show a montage of recent Australian stamp issues.  

A small lot I once saw had been ruined, as strong double sided tape had been used to affix them, and some cretin had roughly peeled them off, heavily thinning each one.

The few others I've seen over the years have mostly had bad foxing/spotting, as many are over 50 years old now, and the cardboard backing is not PH neutral. 

The card they are affixed on appears to be the rather acidic general printer stock.  Not unlike the board stock Asian stockbook pages are made from.  If so, foxing really takes hold in humid storage areas.

Diplomatic staff generally have brief postings to any one location, so this may well explain why full sets or even longish runs are virtually never seen. 

Just bits and pieces here and there, that staffers kept or “liberated” - possibly as little souvenirs of the posting.

Presumably most were tossed away after display, as the stamps being licked down had no more "value" to staff than stamps licked to an incoming piece of mail.

And the value, even if the stamps were floated off,  was just 20c in the typical one shown nearby.

To steal that from the Commonwealth and possibly risk being sacked if detected, would have little appeal to career diplomats I imagine!

Hence the rarity of these cards.  Leading collector Arthur Gray told me assembling these sets is a real "needle in a haystack" endeavour - one here, one there, once or twice a year. 

Then a few turn up somewhere else,  but you already have half of those, making a full collection run of way over 100 different cards a really tough project.