Ham and Egger,
"Philately begins where the catalogue ends"
So it is now in your hands, you can research, chase up information on your covers, and see what transpires.
Please post if you do this, I for one, would like to hear the result on your covers.
What Philately teaches:
As you can see by Floortrader's example, the people behind these stamps, are humans suffering from Greed and Avarice.
Greed is an uncontrolled longing for increase in the acquisition or use: of material gain; or social value, such as status, or power. Greed has been identified as an undesirable behavior throughout known human history.
This should not affect what you personally like to collect or study
just know it exists.
Probably a good idea to drop the slang "Dune" stamps also.
The trucial stamps can be a scholarship of itself.
Fleecing the collector is not only reserved for this geographical area,
it is world wide, Australia is guilty also.
A snippet from Yemen.............