Monsoon morning postage due puzzler

Sometimes rating postage due charges on covers and cards plumbs the depths of postal historians' knowledge.  

Consider these two lovely first issue postal view cards with postage due.

30c Mondorf Postal Viewcard

View 6 - Bridge

Prifix 89-6 Lhbk 84-6

 Luxembourg-Ville to Rollingergrund

11 Jun 1928

Rate:  35c (15 Dec 1927-1 Jul 1930)

5c shortpaid, so correctly charged 10 centimes postage due (double the 5-centime deficiency).

But ...

35c/40c Mondorf Postal Viewcard

View 1 - Vase

Prifix 93-1 Lhbk 88-1 

Esch-sur-Alzette to Bonnevoie

6 Feb 1928

Rate:  35c (15 Dec 1927-1 Jul 1930)

The 35-centime rate was correctly paid.  So why was 30 centimes postage due charged?

My theory:  The card is addressed to Bonneweg "Postfach" (Post Office Box), but no box number is given.  Possibly the recipient did not even have a box at the Bonnevoie post office.  Therefore, a 30c Poste Restante fee was charged to collect the card.

Or was the postage due just a bit of chicanery by the recipient -- Alfons Ennesch, a stamp dealer -- to enhance the value of the card?

What do you think?  

Postage Partially Due - Taxed Under-franked Letter to Germany in 1917

Taxed Under-franked Letter to Germany in 1917

A letter from Diekirch, 23 May 1917,  censored at Trier, to a soldier stationed in Coburg, Germany in 1917.  It is shortpaid 7½c but was taxed 20 centimes ("T" hs and blue crayon "20").  Why?

Under the postal convention of 20 August 1902 with the German Empire, unfranked letters were charged 30 centimes.  This under-franked letter was treated as unfranked less its 10-centime postage, leaving 20 centimes unpaid and payable by the addressee.  Per Lars Böttger, the 20 centimes postage due was converted into pfennig at a rate of 10 Cent. = 8 pfg. -> 16 pfg.; the 16 pfg. was then rounded to 20 pfg.  The conversion to pfennig should have been indicated by the Diekirch post office.

The small circular "porto" marking at the top was probably applied at Coburg.  There are no markings on the back side. 

The cover provides an interesting "sole use" of the 10-centime Marie-Adélaïde definitive!

Belgian Congo to Heffingen - WW1 Returned to Sender 1914-1915

Five-centime postal viewcard sent as printed matter (ms Imprimé) from Bukama, Belgian Congo, 25 Oct 1914, to Heffingen, Luxembourg, returned by the Prisoner of War Censor in London as inadmissible as Luxembourg had been occupied by Germany and Great Britain had declared war on the Central Powers in August 1914.

A Long Journey Back

Postal viewcard dated 25 Oct 1914

Bukama, Belgian Congo, ~25 Oct 1914
to Heffingen, Luxembourg

British red circled P.C. Prisoner-of-War censor

with boxed Retour á l’Envoyeur and
violet sl Undeliverable L.P.S.

[London Postal Service]
 
Lusamba, Belgian Congo, 16 Mar 1915

Kabinda, Belgian Congo, 28 Mar 1915
 
Elisabethville, Belgian Congo, 5 May 1915

Back to Bukama (blue crayon), but then redirected
to Ebo, Belgian Congo (blue crayon)

World War 1 postal history remains a fertile field for research.  Years ago, I hoped that some day we would have a scholarly treatment of Luxembourg World War 1 postal history.  Now we do!  You shouldn't be without Lars Böttger, Handbuch zur Besetzung von Luxemburg im 1. Weltkrieg 1914-1918 und der alliierten Besetzung (2014).