31 Mar 1921
1 Apr 1921
Domestic 20g letter rate = 15c
(12 Apr 1920—1 Apr 1921)
A nice rate cover, but look closer!
15c Marie-Adélaïde with
Antunes and Basien, writing in Luxemburg Perfins (August 2015), state that the Caisse d'Epargne perfin was used from 1905 to 1928.
Although this perfin is not particularly uncommon, uses on cover are scarce.