Why do we see so many covers—all philatelic creations—franked with the 30c Marie Adélaïde definitive surcharged to 17½c in combination with the one-franc surcharged to 87½c? There was no one-franc-five-centime rate, yet dealers often put optimistically high prices on these plentiful philatelic souvenirs.
The explanation is straight forward, and nicely explained in Hans von Rudolphi’s scholarly tome — Handbuch der Briefmarken-kunde: Lieferung 16/17 - Luxemburg, published in 1944. Here is a summary.
In July 1916, two new rates to Germany took effect: a 17½c letter rate and an 87½c rate for parcels weighing up to 5 kg. But to pay the latter rate, the 87½c William IV definitive (issued 6 Jun 1908) was no longer available. This stamp had been surcharged to 62½c on 29 Feb 1912. So to meet the immediate need for an 87½c stamp, Luxembourg on 14 Aug 1916 released the one-franc Marie Adélaïde definitive surcharged to 87½c (the 30c stamp was surcharged to 17½c to pay the new letter rate).
The 17½c and 87½c Marie Adélaïde definitives did not appear until 1 Mar 1917. Thus, the most interesting sole uses of the 17½c and 87½c surcharges are on letters and parcels sent to Germany between 14 Aug 1916 and 1 Mar 1917. And the most challenging use of the two by far is a proper sole use of the 87½c surcharge since very few parcel cards were saved.
The parcel card seen here is illustrative. It’s a proper sole use of the 87½c surcharge with the stamp paying the postage from Luxembourg-Limpertsberg, 2 Nov 1916, for a 950 gram parcel sent to Herne in Westfalia, Germany. The back shows the Luxembourg-Gare 3 Nov 1916 transit, the Trier, Germany, transit of the same date, and the Herne cds of 6 Nov 1916 documenting the arrival of the parcel.
17½c and 87½c Surcharges in Combination