Customers' Choice Paraguay 1940 Inverted Centre ~ Selling Fast [Y16eF7J0]

Registered First Day cover franked with 1940 'Centenary of First Adhesive Postage Stamps' issue (SG 552/555) and 1939 50c black & orange '50th Anniversary of Asuncion University' issue with CENTRE INVERTED (SG 507 variety) tied by boxed 'PRIMER DIA DE EMISION 15-VIII-940' cancels and oval CERTIFICADOS EXTERIOR ASUNCION cancel dated 15 AGOS 1940 with printed registration label alongside. Addressed to ARGENTINA with arrival mark on reverse. Very rare used on cover. 2005 American Philatelic Society certificate accompanies.